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plants possess the essential characteristic of a livingorganism-namely, its power to grow and multiply(as Boycott himself agrees, p. 18) ; in other words, aliving thing can produce more of itself by the incor-poration and assimilation of less complex organicmaterials (food), using these to build up its ownsubstance, this increase being followed in due courseby division. In a living cell, there are plenty ofdead things-inclusions, secretions, excretions, andthe like ; but these are all as dead as door-nails, so faras their power to increase independently of the livingcell is concerned. Further, if, as Boycott admitsmay be the case, these invisible viruses are derivedfrom ordinary living cells, that very fact wouldrender it highly improbable that they themselves aredistinct living entities. In any particular livingthing, whether one of the lowliest cell-units, such as abacterium, or a highly differentiated one, a congeriesof which make up the body of a multicellular animal,we have not the slightest evidence that, in such a unit,there are contained lesser or simpler elements whichsubscribe to the definition of life. Indeed,apart from this, one has-a biologist particularly-an instinctive questioning, quite reasonable, as

Boycott himself allows, whether it is possible for suchminute particles as these invisible alleged organismsto be of sufficient size to contain the large aggregationof coordinated molecules necessary to constitute aunit able to exercise the wonderful functions of life.The reductio ad absurdum to which this " parasitic "view-as, essentially, it would be—would lead usis well shown by a consideration of Gye’s theoryabout cancer, which implies that nearly all the cellsof our body contain, normally, the invisible cancer-organism, a "foreign," intracellular, living element,which is only biding its time until the stimulation ofsome auxetic or adjuvant wakes it into activity !Even Boycott thinks this is an extremely unlikelyidea.And Boycott’s own explanation is, I am afraid,

equally improbable. The pity of it is that he doesnot see where many of his thoughtful and reasonableinferences inevitably lead ! In these admittedlydifficult cases, where we are dealing with minutequantities of substances which we cannot see, it ispertinent to bear in mind one of the essential postulatesin connexion with the vera causa of the old logicians.Is the explanation reasonable, is it likely ? Now it so happens that I myself have devoted a

considerable amount of research to this question andhave come to the conclusion that the virus-diseases,and also malignant growths, are caused by non-livingagents of the nature of ferments or enzymes, producedby the cells. As a matter of fact, I was the first tosuggest this view and to bring forward, during aperiod of over five years, many observations andsustained arguments in favour of a comprehensivetheory in explanation of the same. From the veryfirst (1921) my view, in so far as the question of thetransmissible property of the virus-diseases is con-cerned, was rendered, in my opinion, logically tenableby the very case which Boycott himself cites-namely,that of the bacteriophage of Twort-d’Herelle, whichI regarded as an entirely comparable phenomenon.With regard to this, also, Boycott adopts a somewhatnon-committal attitude. He merely says :

" There are reasons for supposing that this agent arisesin the bacteria themselves ; ... but the data are not con-clusively against d’Herelle’s view that it is really an inde-pendent parasite."

I believe the great majority of bacteriologists areagreed that this agent is a lytic ferment-evenalthough this is not conclusively proved. In thecase of virus-diseases, my theory assumes that thecharacter of the normal blood-digestive enzyme hasbeen altered by reason of the faulty vital activity ofthe cell, this pathological derangement having beeninduced at the outset by the infection with the virus -i.e., that particular modification of the normalenzyme in question. And it is very gratifying to seehow Boycott is led to inferences which I have alreadydrawn in certain of my papers. For instance, when

considering the possibility that " fresh " virus maybe made by each infected person or animal, he saysthat it is just possible that such diseases (he instancesmeasles or distemper) were originally brought intoexistence by causes quite different from those whichnow maintain them. Similarly, I consider that theseviruses have probably originated autogenetically,the pathological hsemetaboly having been induced inthe first place by some outside cause, such as, in somecases, a very unusual manifestation or syndromeassociated with an ordinary bacterial infection.1 Imay just mention two interesting possible examples,in a transitional phase, as it were, that is, developingat the present time, though these are still admittedlylittle more than speculations or notions, as Boycottputs it. They are encephalitis lethargica, and thevirulent, devastating type of influenza; but here,too, lack of space precludes any consideration ofthem. Again, Boycott admits that if these virusesare the product of abnormal cell-activity, havingonce arisen, it is by no means impossible that somecan arise de novo, nowadays, given the necessaryconditions. (This is a very different thing, it must beborne in mind, from the creation of a new livingorganism, apart from an existing one !) And, indeed,as regards at least one type of stabilised, regularvirus (if I may so put it), namely, typhus and itscongener, trench-fever, the fresh origin of such virusby pathological haemetaboly in its primary host, thelouse, is, I venture to say, very much more than a merepossibility.

Just because it is so apparent from Boycott’sarticle that the only alternative to a causal organismin the case of the virus-diseases and of cancer is aferment, and because I was the first to put forwardthis view, as a result of my own work on the importantfunction of normal blood-digestion and its variousderangements, I have thought it worth while totrespass on your space.

I am, Sir, yours faithfully,H. M. WOODCOCK.

Walton-on-Thames, Jan. 14th, 1930.

TESTS FOR MOTOR-DRIVERS.

To the Editor of THE LANCET.

SIR,—It is surely essential that a motor-drivershould not be given a licence to drive till he hasfurnished a certificate that he is free from such agrave disability as to render him totally unfit to bea chauffeur. There are many men with very defectivevision in one eye or partially deaf who are unawareof the fact, and many others who will not admit thedefect.The Road Traffic Bill, as amended in Committee

(Clause 5, p. 6), accepts the applicant’s declaration asto freedom from disability. In the interests ofhumanity, and for the safety of the public, I suggestthat some test (neither severe nor expensive) shoul dbe insisted on for every applicant for a licence todrive a motor. A simple form might be filled in andsigned by a doctor at a modified fee, paid by theapplicant. The amount of the fee might be settledby the State. Are-examination and certificate neednot be annual.As one of the delegates I raised this point at the

Conference on Street Accidents, convened by theMinister of Transport on Jan. 14th and 15th, whichwas supported by Mr. A. Hume Nicholl, Chairmanof the London " Safety First " Council. The onlyarguments advanced against a test were on thescore of expense and impracticability.

I am, Sir, yours faithfully,D. A. COLES,

Chairman of Council of Industrial Medicine ; Vice-Chairman of London " Safety First " Council.

Beckton-gardens, E., Jan. 17th, 1930.

1 And, ultimately, it should be added, cellular autolysis, whichis probably, in most cases, the end-result as regards the affectedcells.