No. 4781.

APRIL 17, 1915.

An AddressON

WOUND INFECTIONSAND ON

SOME NEW METHODS FOR THE STUDY OFTHE VARIOUS FACTORS WHICH COME INTOCONSIDERATION IN THEIR TREATMENT.

Delivered before the Royal Society of Medicine on March 30th,

BY COLONEL SIR A. E. WRIGHT, M.D.,F.R.S.,

A CONSULTING PHYSICIAN TO THE EXPEDITIONARY FORCE.

(From the Research Laboratory attached to No. 13 GeneralHospital, Boulogne-sur-Mer.)

(Continued from p. 741.)

What are the Factors which Influence the Emigra-tion of White Blood Corpuscles into the Wound?I PASS now to consider yet another subject-matter

-the emigration of leucocytes into the wound. Ineed not labour the point that this is a factor whichmay determine the issue of an infection; nor

need I point out that it behoves us to acquire acontrol over the movement of leucocytes, and thento turn this to account, as the case may be, by acti-vating or restraining emigration.Broad foundations for our work have, as you

know, already been laid by the brilliant researchesof Metchnikoff. But it was with Metchnikoff alwaysa question of experiments in vivo-that is, of ex-periments carried out under conditions whichcannot be sufficiently simplified to give quiteunambiguous answers. And we require for theelucidation of our problems and for all detail workconnected therewith, absolutely simple crucialexperiments, such as can only be made in vitro..The line of thought which I have followed in

elaborating a laboratory method for the study ofthe phenomena of emigration is the following :-The leucocytes in extravascular blood are knownto retain their emigrating power. A difficulty will,however, when we are working with extravascularblood, attach to our observations by reason ofthe fact that we have not at disposal such a con-taining membrane as the capillary wall. We are,in fact, in dealing with extravascular blood con-fronted with a situation similar to that which wouldbe encountered in observations in vivo if the

capillary walls were to give way, and we had tomake observations on emigration in a portion oftissue which was flooded out by red corpuscles.

I had hoped at first to be able to circumvent thisdifficulty by taking advantage of the fact that when Iclotting occurs the red blood corpuscles becomeenclosed in a meshwork of fibrin, after the mannerof fish in a net. But all my efforts to make thefibrin meshwork take over the office of a contain-ing membrane were defeated. No matter howtenderly the clot was treated the meshes of thenet broke, and haemorrhage from the clot interferedwith the observations.A second difficulty also presented itself. When

in the living body white corpuscles emigrate intoconnective tissue it is possible to register theirtravel because they move forward through a retain-ing meshwork. It would not be possible to do soif they merely passed out into fluid, to be after-wards carried hither and thither by every chanceconvection current. Exactly the same applies to iNo. 4781.

the extravascular blood. The emigrating leucocytemust be provided with some sort of scantlingto move forward upon, and come to rest in.

After a time I alighted on a method whichsatisfies the two aforementioned experimentalrequirements, and which, as I think, provides allthat is required for a quantitative estimation ofemigration. Let me first tell you the general linesupon which the method proceeds, and then set outthe details of the technique.

Principle of the Method Employed for making,

Observations on Emigration.The principle of the method is as follows:-We

fill in a capillary tube with blood from a prickin the finger, immediately place the capillary tubein the centrifuge, and centrifugalise until wehave carried down all the corpuscles. We havenow in the upper half of the tube a plasma whichhas been completely freed from all formed elements;and in the lower half of the tube, at the bottom,the red blood corpuscles intermixed with a certainnumber ’of polynuclear white blood corpuscles ; andabove this a layer made up predominantly ofwhite blood corpuscles-these last in the front ranksconsisting almost exclusively of small and largemononuclears. The blood now clots. And thisgives in the upper half of the tube a clot con-

sisting of fibrin -without any formed elements-let us call this the white clot-and in the 10weJ?’ ;half of the tube a clot-let us call this the redclot-which holds all the corpuscles in its meshes: :When a chemotactic stimulus now comes into, appli-cation from above the white blood corpuscles willcome out from the red clot and will travel upwardsthrough the meshes of the white clot-afterwardsmaintaining their positions so as to allow of, ourmaking measurements and enumerations. We willnow pass to the details of the technique.

Details relating to Apparatus and Procedure.With regard to apparatus, all that is required

is a supply of flat capillary tubes. By usingflattened capillary tubes we obtain a thin clot,which can more easily be examined under the

microscope.FiG. 5.

Method of making emigration tubes. A, Method of givingthe flattened conformation to the capillary stem. B, Methodof binding the tube round to form an elbow.

We make these tubes-and they may convenientlybe called emigration or chemotactic tubes-eitherout of a small test-tube, or out of a length of fairlywide-bored glass tubing. We heat in the blowpipeflame until the glass becomes very plastic; then,making a sharp outward turn with the right wrist,bend the tube round through a right angle, givingit the proper flattened conformation; and then draw Jout into a long flat capillary stem. (Fig. 5, A). Wethen cut this through at the point where it beginsto lose its flattened conformation; and so leaveattached to the next segment a sufficient lengthof tube to take hold of when we go to work upon

Q

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it. When a sufficient number of lengths of flattenedstem have been provided, we cut these up intosegments of about 8 cm. in length; arrange themside by side after the manner of a palisade; andthen with our glass writing pencil rule two linesacross the face of our tubes. The first of these linesought to fall somewhere in the middle. It is toserve as a fiducial mark for filling in the blood fromthe finger. The second line, which may convenientlyfall at a point to about half or three-quarters of acentimetre to the end of the tube, is to serve as afiducial mark in filling in the chemical agentwhose effect we are to study.The tube may now be used just as it is : or we

may before using it furnish it with a syphon-curveby bending it round at the level of our secondfiducial mark. We do this by taking up each tubeseparately, holding it horizontally, and then

passing it rapidly to and fro through a small by-pass flame. The action of gravity will then, as

soon as the glass softens, bend round the tubefor us. (Fig. 5, B.)Method of Using the Emigration Tubes and Bring-

ing the Chemotactic Agent into Application.The emigration tube is first filled in up to the

midway point with blood drawn from a puncture inthe finger. In the case where we employ a benttube this is done by letting the blood flow in throughthe syphon curve.The chemotactic agent can now be brought into

application in three different ways.1. It may simply be superimposed upon the clotted

blood. This is done by using a filiform pipette,made by heating the stem of an ordinary capillarypipette in a small by-pass flame and drawingout, while we with a rubber teat apply internalpressure to prevent the walls of the hair-fine tubecollapsing. Considered as a method for bringing achemotactic agent into immediate application, thismethod falls short in the respect that the chemicalhas to diffuse down through the whole white clotbefore it comes into operation. In view of this, themethod does not lend itself to the institutionof any comparisons between normal blood andaneamic blood. For the experimental conditionsare not comparable when our chemotactic agenthas, in the one case, to diffuse through a lengthcorresponding to half the column of blood ; and,in the other case, through a length which mayamount to nine-tenths of that column.

2. The second method of bringing the chemo-tactic agent into application is that of super-imposing the chemotactic agent upon the unclottedblood. (Fig. 6, B and c.) Having filled in a

curved emigration tube up to mid-point markwith blood; we tilt the tube so as to take ina dividing bubble of air; then fill it up as

far as the elbow with the chemotactic agent;and then, after sealing up the distal endof the tube, proceed to centrifuge. This methodis applicable, in particular, when we are work-ing with bacterial suspensions; for while thewatery suspending fluid remains, by reason of itslight specific gravity, on the top, the microbesare, by virtue of their higher specific gravity, carrieddown into the plasma, to be embedded in the whiteclot all the way down to the leucocytic layer.

3. The thi1’d method is the method of traversing.(Fig. 6, D and E.) In employing this we may useeither a straight or a bent emigration tube. Wefill in, first, with our column of blood; thenfollow on with the dividing bubble of air; and

then, making use of the forerunning column ofblood to serve as a brake, fill in up to thefiducial point with the chemotactic agent.l Finally,we seal up that end of the tube which has servedas an inlet and place the tube in the centrifuge.

FIG. 6.

A t5 u L J!)

’I Method of adding chemotactic fluid to blood. A, Curvedemigration tube, empty. B, Tube filled in with a columnof blood, a dividing air bubble, and then, as far as the elbow.with a bacterial suspension. c, Tube after oentrifugal-isation. The bottom of the tube is occupied by the "redclot," and the intermediate portion by the "white clot"and implanted bacteria; at the top is the waterymenstruum in which the bacteria were suspended. D,Tube filled in for traversing. In the lower portion of thecapillary stem is the chemotactic agent; in the upper partthe column of blood. E, Tube after centrifugalisation. Thebottom of the tube is occupied by the "red clot"; theintermediate portion by the " white clot," containingtraces of the chemotactic agent. At the top the waterymenstruum containing the bulk of this agent.

Our chemotactic agent will now traverse thecolumn of blood and take up a position at the

top, leaving behind it in the plasma traces of what-ever chemical it holds in solution. That this iswhat actually happens, can be shown by employing,in place of a colourless chemotactic agent, a solu-tion of methylene blue, or simple water. This last,when it follows on after a column of blood anddissolves the red blood corpuscles which thisleaves in its wake, will come out at the top colouredwith hsemoglobin.The traversing procedure will be applicable in

the case where we want to bring into operationchemical agents, and especially applicable where wewant to bring such agents into instant application.When we are working with a series of tubes, as

will practically always be the case, it will be wellto place each, as soon as it is filled, into icedwater, or ordinary cold water. The buckets of thecentrifuge will serve as convenient receptacles.After centrifugalisation the emigration tubes areplaced in the incubator, according to circumstances,for from three to twelve hours or more. While inthe incubator the tubes may conveniently be placedupright-i.e., with the white clot uppermost-inplasticine. They may also be laid on their sides,tilted a little upwards. The inverted position isto be avoided. For when we invert our tubes we

1 In practice the procedure of traversing is to be carried out exactlyas here described. In the illustration, Fig. 6, D, in order to convey theidea of traversing to the eye, the chemotactic agent precedes insteadof following the column of blood.

789

bring down into the white clot a shower of redcorpuscles which block emigration, and also obscurethe view.

Method of Bringing the Emigration Effect intoView and taking Cognisance of the Results.

When all we want, is to get a general idea ofwhat is going on in the tubes, we can obtainthis by introducing the unopened tube into anobservation cell. A very simple form of observa-tion cell can be made by placing small pellets ofplasticine upon each of the four corners of a

microscopic slide, covering in with another slide-allowing a little overlap-and then fillinginto the interspace either water or some more

highly refractive fluid, such as glycerine or oil.

By observing in such a cell we bring into viewnot only the leucocytes which have emigrated intothe white clot, but also those which have escapedinto the interspace which may develop betweenthe clot and the walls of the capillary tube.2For all purposes of quantitative observation we

blow out our clots into water, wash carefully so asto remove leucocytes adhering to their exterior,and then mount them on a slide. We then, aftercutting off the surplusage of red clot, fix by drying,and stain for a few minutes in Euhne’s methyleneblue freely diluted. The specimens are examined,first, dry or in water, under a low power objec-tive, and afterwards in oil under an immersion.(See Fig. 7.)General Considerations relating to the Movements

of White Blood Corpuscles.Before passing to consider the question how it

will be possible to arrive at a quantitative expres-sion for the leucocytic movements induced by achemotactic agent, it will be well to take a generalsurvey of the things that present themselves toview in every emigration tube.We have to take into account in connexion

with white blood corpuscles two kinds of move-ments. We have, on the one hand, a processof wandering at large; and, on the other hand, adirected movement-i.e., a movement along someparticular axis-undertaken under the direction ofa, chemical stimulus. We may call the first kind ofmovement an eleutherotropic movement. Thesecond is usually known as a chemotactic-I preferto call it a chemotropic-movement. It is, of course,the latter, not the former kind of movement whichwe are here primarily concerned to study. For

2 Attention may, in connexion with this, be called to facts whichhave an importance and a useful application in medicine, whichhappen to have also an importance and a useful application inconnexion with the emigration method here under consideration.The facts I have in view are as follows. The blood of a personsuffering from chilblains, or any other manifestation of a

lowered blood coagulability, will, on centrifugalisation, generallyfail to give the kind of white clot we require for our emigra-tion experiments—i.e., one that is firm and non-contractile. Thiscondition of things can be remedied by the exhibition of calciumsalts, or, as the case may be, by appropriate additions of thesesalts made to the blood when filling our capillary tubes. I would inconnexion with this emphasise that we have here brought into clearview what is the really material factor in connexion with the effectexerted by calcium salts in the blood.And I may perhaps be permitted to point out, in connexion

with my own work on calcium as an agent for promoting and citricacid as an agent for diminishing coagulability (Brit. Med. Jour.,July 29th, 1893, and July, 1894; THE LANCET, Jan. 18th, 1896, andJan. 30th, 1897), that while what I have said with reference to theclinical effects exerted has been, I believe, universally confirmed andaccepted; what I have said with respect to the effect on thecoagulability of blood in vitro has been traversed. This stands, asI believe, in relation to the fact that the laboratory workers whohave repeated my work have employed methods which tookinto account rapidity, but left out of account firmness, of coagula-tion. It will now, I hope, by adopting the method of centrifugalising,and watching the effect exerted upon plasma which has been disem-barrassed of corpuscles, be possible to arrive at unanimity in thesematters. Finally, I may direct attention to the fact that what comesinto view in ceatrifuged, is seen also in uncentrifuged, blood. Whenwe make to this appropriate additions of calcium salts we obtain, as Ilong ago pointed out, a firmer and non-contractile clot.

clearly it is the chemotactically directed movementsof the leucocytes towards the bacterial focus, andnot their wanderings at large, which come intoconsideration in any conflict against infection.None the less, a word may be said about

eleutherotropic movements. One finds in everyspecimen of blood which has been simply centri-fugalised and placed in an incubator, always acertain wandering at large of the leucocytes-in particular, the mononuclear white blood cor-puscles, which have been tightly packed togetherby the action of the centrifuge and are rangedat the top of the red clot, leave their ranks andwander out into the adjacent regions of the whiteclot. The polynuclear leucocytes also are affectedby eleutherotropic wandering. They come out fromthe hinder ranks of the leucocytic layer, and alsofrom deeper down in the red clot, and wander free.In our observations we leave out of account allthose leucocytes that have wandered outside thewhite clot. We regard them as having run towaste.

FiG. 7.

N, --. ,.c L ’.r-- -.

A JB C JD g’ z

Clots from emigration tubes blown out and mounted: A, noemigration; B, compact emigration; o, dispersed emigra-tion ; D, method of enumerating leucocytes which haveemigrated; F., bacterial colonies coming up only in portionof clot which has not been reached by the emigratingleucocytes.

A further point which claims attention in con-nexion with emigration is the nature of the

emigrating leucocytes.Ordinary eleutherotropic emigration is predomi-

nantly mononuclear, this being probably accountedfor by the fact that the white blood corpuscles whichare ranged up along the line which divides thered from the white clot are almost all mononuclear.In chemotactic emigration we have either a diffe-rential emigration of polynuclear white corpuscles,or a mixed mononuclear and polynuclear emigra-tion in which either the one or the other of thesevarieties of leucocytes may predominate. In all suchmixed emigrations the polynuclear, presumablybecause they are faster of foot, overtake the mono-nuclear, leucocytes and pass on and occupy themore distal portion of the field of emigration.Method of Arriving at a Quantitative Expression

respectively for Compact" and dispersedEmigration."

A quantitative expression for the emigrationmovement which takes place in a capillary’tube can be arrived at in two ways. When we are

790

dealing with a compact emigration (Fig. 7, B)- "Bthat is, where the, field of emigration is quite (

closely packed with leucocytes-we have simply to i

measure the area of that field, or (and this answers ’1the purpose perfectly well) the length of clot roccupied by the emigration; and we may con-veniently measure it in terms of microscopic fields. IIn such measurements we take off from the base- <

line furnished by the distal border of the cone of i

leucocytes which occupies the base of the white <

clot.’ This represents the original leucocytic layer c

converted, by the contraction of the fibrin, into a Jcap covering the upper end of the, red clot. c

(Fig. 7, c.) . c

When, as will happen when a longer time hasbeen allowed for the wandering out and dispersionof the leucocytes, we have before us a dispersedemigration it will no longer suffice simplyto measure the distance the leucocytes have Itravelled into the clot. It now becomes necessaryto enumerate the emigrating cells. Employing first Ia low power lens, we bring the upper edge of thecap of leucocytes to the extreme edge of our’fieldof view. Then turning to our oil immersion, webring this down upon the central portion of the

low-power field, and make a count of all the

leucocytes which lie within its purview-whennecessary, helping ourselves out in our count, byintroducing into the diaphragm of our eyepiecea cover-glass divided up by light rulings,made with a glass writing pencil. Havingobtained in this way a value for the emigra-tion in an arbitrarily selected portion of thefirst microscopic field, we go back to our low-powerobjective and move our specimen along until theobjects on the extreme distal margin have beencarried right across the field, and now lie just outof view on the other side. The further steps inthe procedure are now simple repetition.What are obtained by this method of enumera-

tion are, of course, only arbitrary figures, and itwill be realised that the comparative values arrivedat will be strictly accurate only where we areemploying clots of similar thickness.

Survey of the Data which the Method has AlreadyGiven.

We may now pass on to consider some of the datathat the method has already given. White bloodcorpuscles will move out in any direction towardsa chemotactic substance. They will, however,emigrate more freely downwards, than horizontally;and more freely horizontally, than upwards.Anaerobic conditions are more favourable to

emigration than aerobic conditions. Leucocyteswill travel out further in the direction of a chemo-tactic substance when we absorb the oxygen in thetube with caustic alkali and pyrogallic acid andseal, than when we leave the end of the tube opento the air.

Leucocytes emigrate more abundantly in tubesstanding at a temperature of 40&deg; C. than in tubes

standing at 37&deg;. They do not emigrate at tem-

peratures of 10&deg; to 15&deg;-the temperatures whichprevailed on our laboratory bench. After exposureto temperatures of 0&deg; C. for periods of half to onehour they emigrate apparently as freely as before.Emigration apparently goes on unaffected in the

presence of ether. It is abolished or suspended inan atmosphere of chloroform.

Physiological salt solution, brought into applica-tion either by traversing or by superimposing itupon the clotted or unclotted blood, induces a very ,’

vigorous emigration of polynuclear white blood

;orpuscles. Weaker salt solutions induce a lessvigorous emigration, and water again a less’vigorous. Strong salt solutions-for example 5 per’3ent. salt solutions-suppress emigration. ,

It will be appreciated in connexion with theseand all findings obtained by this method, that theydo not tell us the effect of reagents acting in thespecified dilutions direotly upon leucocytes, butDnly the effect of these reagents operating from a,listance. In other words, our experiments do notEurnish information as to what would be the effectof bringing the chemical agents in the specifiedconcentrations directly in relation with the capil-lary wall.

Bacterial suspensions which have been sterilisedby heating evoke, according to the dilution inwhich they come into application, quite differenteffects. The general rule applying to bacterial

suspensions would seem to be as follows. Con-centrated suspensions usually completely suppressemigration. Ten or hundredfold diluted, thesesame suspensions evoke vigorous emigration. Whenwe employ progressively higher dilutions we arrivein time at a point when the effect of the bacterialsuspensions is exactly the same as those of thearticular fluid which we are employing as a diluent.Normal bloods tested with one and the same

series of bacterial suspensions exhibit quitedifferent degrees of chemotropic sensibility..Chemotropic sensibility, not: alone to bacterialsuspensions but also to physiological salt solution,,is very strikingly modified in the case of patientssuffering from bacterial infections. The same

applies to persons inoculated with streptococcicvaccines. In five out of six men, inoculated withsuch a vaccine and examined both before and after-wards, the emigrating response to streptococcuswas subsequently to inoculation very strikinglyincreased. In the case of one man it was

diminished.Results somewhat similar to those obtained with

dead cultures are obtained with suspensions ofliving microbes (streptococci and gas phlegmonbacilli), but here the prolonging of the incubationperiod may strikingly alter the situation.What generally happens may be summed up as

follows. When, by superimposing and centrifuging,a heavy sowing of microbes has been implantedinto the unclotted blood, the colonies come up allalong the white clot, and emigration into this iscompletely checked. Where only a moderate im-plantation of microbes has been made, we have indifferent parts of the clot different results :-Bacterial colonies develop freely in the distal area.of the clot which is not invaded by emigration. Inthe intermediate region-that is, in the regionwhere the microbes can grow out before the leuco-cytes arrive-one sees with the low-power objectiveareas specially crowded with leucocytes-these arein point of fact colonies which are being brokenup and dispersed by invading leucocytes (Fig. 8);-and with the oil immersion one sees that everyleucocyte in these crowded masses is taking upmicrobes, and that there is also in all this regionof the clot plentiful phagocytosis of scatteredmicrobes. (Fig. 9.) In the base of the white clot-i.e., in the area where emigration has occurredearliest and most vigorously-one finds absolutelyno trace of microbial growth.The appearances which have just been described

correspond, of course, to a period of conflict. Thisconflict is generally at its most interesting phase in

791

tubes which have been incubated from three to sixhours. When we come later&mdash;for instance, after12 or more hours-the conflict is over. We thenAnd either that the white corpuscles are mastersof the field, and the microbes have disappeared, orelse that the microbes have invaded the whole clot,and that this crumbles away as soon as it isblown out into water. There can be little doubtthat the crumbling away of the clot, and the over-running of the blood with microbes are due to thedigestion of the fibrin, and the corruption of theblood fluids by trypsin set free from the dis-integrated leucocytes.

FIG. 8.

Extreme limit of emigration, showing phagocytes attackingstreptococcus colony.

Egperiinents such as these just outlined in whichliving microbes are brought into application onblood provide in point of fact a valuable testmethod. They tell us the resultant of the chemo-tropic sensibility of the leucocytes, the opsonic powerof the blood fluids, the digestive capacity of thosephagocytes which come into action, and of the anti-tryptic and, where such comes into account, thebactericidal power of the blood fluids. We are, infact, furnished with something like a completeevaluation of the antibacterial powers of the blood 3There is still one element left out of account.The test method here in question does not tell usanything as to whether or no there are bacterialpoisons in solution in the blood fluids of theinfected man. But this is a question which can beseparately investigated. I have tried to find theanswer by traversing normal bloods with the seraderived from patients suffering from septicaemicinfections. And I have by this procedure obtainedin a series of cases what appeared to be a definitelychemotropic emigration.

All that has been recounted above is, of course,only a very small beginning. But I think we maybe confident that the method for the study of

emigration which has here been proposed willresolve important problems in connexion withinfection generally, and also-and this is whatspecially concerns us here-some of the problemsin connexion with wound infections which are nowurgently pressing for a solution.

3 It will be observed in connexion with tests thus conducted withcentrifuged blood that, if we leave out of regard the centrifugalisation,they are in all essentials the same as the phagocyto-bactericidaltests with freshly drawn uncentrifuged blood which I have alreadydescribed (Vaccines and Drugs in Pneumonia, Constable, 1914).

In the matter of general problems of infectionit would, 11 think, be possible, by implantingbacteria into blood in combination with chemicalagents which would respectively promote andhinder emigration, to resolve for each particularbacterial infection, the question as to whether it isthe leucocytes or the blood fluids which come mostinto consideration as destructive agencies. Thatproblem once resolved, we should know whetherwe ought in the infection in question to direct ourchief efforts to increasing the efficacy of the bloodfluids, or to modifying the chemotropic sensibilityof the leucocytes and encouraging emigration. ’" --

Again, it looks as if it might be possibleby very simple experiments to resolve theproblem as to why in gonorrhoea, and also in othersurface infections, the purulent discharge issuddenly arrested when ,the microbes succeed, ininvading the blood stream, or establishing them-selves in an articulation or elsewhere in theinterior of the body. It would seem possible-forsomething of this sort would seem to occu , insepticaemias supervening on wound infections-that we may be dealing here with a paralysis of theemigrating powers of the leucocytes. Or, again,it is possible that in these cases emigrationmay be simply suspended by a redistributionof the chemotactic forces. In other words, thecessation of the external discharge may simply,mean that there is now in the blood a bacterialpoison; and that this chemotactic element, actingupon the leucocytes as a vis a tergo, counter-balances the vis a fronte of the chemotactic sub-stances produced by the bacteria on the externalsurfaces.

FM. 9..

>

Phagocytosis of streptococcus towards extreme limit ofemigration.

In connexion with the particular problems ofwound infections we may hope at no distant dateto come into possession of information which willenable us to activate or restrain, according as theone or the other may approve itself the betterpolicy, the emigration of leucocytes into the wound.And we may hope also to determine in connexionwith every antiseptic or other solution which is

brought into application in a wound, whether itpromotes or hinders emigration.

Finally, let me point out=for everything thatconcerns bacterial vaccines concerns the treat-ment of wound infections-that experiments onemigration will almost certainly’ resolve a

number of important outstanding questions in

792

connexion with vaccines. They ought very easilyto resolve the question as to what is the bestexcipient for a vaccine-whether a menstruumwhich would restrain emigration, or one, likephysiological salt solution, which would call fortha vigorous emigrating response at the point of

injection. And lastly-and this would be one ofthe most important applications of observations onemigration-we ought to be able to determinewhat is in the case of each bacterial vaccine thedose which will induce the earliest possible andthe most effective determination of phagocytes tothe focus or foci of infection.

(To be continued.)

ON THE PENETRATING POWER OF THEX RAYS FROM THE COOLIDGE TUBE.

BY SIDNEY RUSS, D.Sc.

A Coolidge X ray tube having been acquired bythe electro-therapeutical department of the Middle-sex Hospital, Mr. C. R. C. Lyster requested me tomake some measurements of the radiation emittedfrom it, preparatory to its being put into clinicaluse. The results of a first systematic series of testsupon it were communicated to the February meet-ing of the Roentgen Society. The leading featuresof the observations were : (1) The recognition thatthe unscreened radiation from the bulb was hetero-geneous, consisting of " soft," "

medium," and" hard" rays; and (2) the relatively larger pro-

duction of " hard rays than of " soft " rays whenthe heating current, regulating the cathode stream,was increased.

Since the meeting referred to, the observationson the bulb have been continued with two objectsin view-first, to measure the hardness of the rayswhich would be used clinically (for superficial andfor deep-seated conditions) ; and, secondly, to findhow nearly the most penetrating rays given outfrom the bulb approach the penetrating power ofthe hard gamma rays from radium. It was assumedthat for superficial conditions unscreened " soft "and

" medium" rays would be used, and that for

deep-seated conditions the rays would be heavilyfiltered by aluminium; accordingly measurementswere made of the character of the rays under thesecircumstances. This was done by finding how theintensity of the beam of X rays was reduced oninterposing sheets of aluminium between the bulband a small gold-leaf electroscope used to measurethis intensity.When measuring the unscreened rays the bulb

was run under a moderate sparking distance (3 cm.between spheres 5 cm. in diameter, correspondingto about 11 cm. between points). The gradualreduction in the intensity of the radiation as in-creasing thicknesses of aluminium are interposedis shown in Curve 1, Fig. 1. When this curve isanalysed it is found to consist of approximatelythree portions, which may be considered as

Section D, in which the rays are "soft" " andtherefore easily absorbed; Section E, where theyare rather more penetrating ; and Section F, wherethey are considerably

"

harder." The beam is, asstated, heterogeneous.The observations upon heavily screened rays

were made as follows. For the same heatingcurrent as before the spark-gap was increased tonearly the limit of the coil (viz., 10 cm. between the

spheres or 30 cm. between points) and the rays werescreened by 7 mm. of aluminium. The character ofthe rays which penetrated this filter was found inthe manner described, and the absorption sufferedin going through various thicknesses of aluminiumis shown in Curve 2 of the same figure. Analysis ofthis curve shows that the rays are very hard andpractically of a homogeneous nature.The introduction of as much as 7 mm. of

aluminium for the purpose of screening effects a.considerable reduction in the intensity of the rays,,but, granted that at least 3 or 4 mm. are necessary,.it remains to determine whether the extra amountof aluminium, by which homogeneity is attained.,entails too large a reduction in the quantity ofrays available for use; the beam is not quite homo-geneous with 4 mm. screening. Actually it is foundthat this extra 3 mm. entails a diminution of nearly25 per cent. in the intensity of the beam alreadyscreened by 4 mm. of aluminium. Apart from anydesirable physiological effects which the hardestX rays may give rise to, the use of a homogeneous.beam ensures the most uniform irradiation through-out the tissues that is possible, assuming that suchapplication has to be made externally; moreover,.it allows of an accurate determination of the

strength of the radiation at any particular depthof tissue.The results represented in Fig. 1 were obtained

by using aluminium as the absorbing substance forthe rays ; this is a matter of convenience, for thepure material is obtainable in sheets of any requiredthickness. When it is desired to apply the data tmdetermine the gradual loss of intensity of X raysas they make their way through the tissues certainprecautions are necessary. If we consider that the

FiG. 1.

tissues of the human body have on an averageabout the same density as water, then if we knewthe relative transparency of water and aluminiumfor X rays of any specified quality we could gaugethe absorption which the tissues would exerciseupon any particular beam of X rays.When experiments are made to determine this.

relation between water and aluminium it is foundthat in the case of soft X rays water (and thereforetissues also) absorbs them much less than its.density would suggest, actually about one-fourthpart; hence, since aluminium is 2"7 times thedensity of water, 1 mm. of aluminium absorbs as

much 4 X 2’7 = 10’8 mm. of tissue. As one passesto rays of a more penetrating character waterbecomes relatively to aluminium a better absorber,