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SOUTH AFRICAN MINE DUST.

IT is some years since the pioneer methods of dust-sampling as practised in the South African gold minesfirst attracted and held the attention of those interestedin the study of silicosis. There are two methodsconcerned-namely, the gravimetric (or sugar-tube)method in which dust is weighed, and the so-calledkonimetric (Gr. &kgr;&ngr;&sfgr;, dust) method in which the

particles are counted with the aid of a microscope.General confidence in these methods has apparenlydiminished because the gravimetric returns, thoughreliable within their limitations, did not afford thenecessary information ; while lack of correlationbetween the konimetric returns of different observersor groups of observers, and their not infrequent lackof correlation with simultaneous gravimetric returns,has shaken confidence in this the alternative method.In a well-illustrated monograph, which has recentlycome into our hands, a group of workers at theSouth African Institute for Medical Research reviewthe position as it appears to them on the Witwaters-rand, and present their most recent technique forstandard routine sampling in the mines whilst actuallyat work.

Dr. Mavrogordato states that, in 1911, 25 per cent.of employees contracted silicosis, developing the sym-ptoms within a couple of years; in 1917 only about6 per cent. of workers were affected by the disease,and they were now taking from nine to ten years todevelop the symptoms ; and in 1922 less than 3-5per cent. of the men employed were contractingsilicosis, and they required from nine to ten years todevelop symptoms. He also points out that theresults of " dust surveys " in 1915 registered by thegravimetric method an average of 4-9 mg. of dustper cubic metre of air, whereas in 1919 the averagehad fallen to 2-9 and in 1923 it was only 1-3. It isobvious, therefore, that the diminution in the amountof silicosis has gone hand in hand with the diminutionin the dust content of the air, as measured by theirmethods, and this fact should give confidence in thevalue and reliability of these methods. He is verycareful to make clear that the routine methods atpresent in practice, although the best available underactual working conditions in the mines, are by nomeans perfect, and there are still difficulties to besurmounted. Dr. Mavrogordato prefers the koni-metric method for routine sampling to the gravimetricmethod because the former is less trouble, demandsless skill and less equipment, while at the same time itgives more prompt returns. In taking the sampleof dust the konimeter (Kotzé or circular pattern)causes a small volume (5-10 c.cm.) of air to pass at ahigh and definite velocity, through a standard narrowjet, and to impinge upon a glass slide covered withadhesive material (glycerine jelly). The dust particlesare counted with a microscope giving a magnificationof x 120, using a fixed and standard illumination, andalso a special arrangement of stop and condenser toobtain a definite dark-ground illumination so as toevade the ultra-microscopic effect as far as possible,since ultra-microscopic particles of silica are eitherinnocuous or non-existent ; large particles of silica arealso comparatively unimportant, the particles pro-ducing silicosis measuring from 5µ-0.25µ. When it isthe latter alone that would have to be counted by aperfect method, the difficulties in the way of intro-ducing such a method are obvious. Nevertheless thestandard routine described is considered to yieldsufficiently approximate returns with a minimumdemand on the operator. The drawback of themethod is that it measures the total air-borne particlesbut not necessarily silica ; the complications intro-duced by carbon, by fog, and by water-soluble

1 Publications of the South African Institute for MedicalResearch, edited by W. Watkins-Pitchford, M.D. No. XVII.,The Value of the Konimeter—being an Investigation into theMethods and Results of Dust Sampling as at Present Practised inthe Mines of the Witwatersrand. By A. Mavrogordato, M.A.,M.R.C.S., L.R.C.P., with the collaboration of J. Boyd, J. Innes,E. MacEwen, A. Pulford, L. G. Ray, G. D. Maynard, J. Moir,E. Cluver. Johannesburg. 5s.

particles have also to be considered, and some

measures to overcome these troubles are described.Dr. Mavrogordato and his colleagues do not restsatisfied with the present routine methods, and theyhope to obtain the help of the dust-sampling com-mittee of the Chamber of Mines, of the Mines Depart-ment, and of the Mine Officials to enable them to testmore recently introduced technique, not only in alaboratory, but, what is of more importance to them,also under actual working conditions of the mines ;these recent methods include Palmer’s method,Read’s method, Greenburg and Smith’s method,Owen’s method, and the electrical precipitationmethod. Dust, of course, collects in the air of mines,owing to absence of efficient through ventilation ;local ventilation is of no value. Dr. Mavrogordatosuggests that Dr. Leonard Hill’s kata-thermometer,because it is able to detect ventilation currents andestimate velocity of air movement, may give moreinformation as to undergound health conditions thanany other single procedure ; but we will require toknow the minimum linear velocity which will keepdust diluted and which will dissipate any dust pro-duced owing to some failure in the usual precautions.

It may surely be regarded as very creditable to havereduced the number of cases of silicosis from 25per cent. in 1911 to less than 3-5 in 1923, an improve-ment which is attributed to the use of water toprevent dust production and also to some attempt toremove dust by mechanical ventilation. To reducethe case-incidence further, some fresh factor or

factors must be introduced. Dr. Mavrogordatosuggests (1) systematic through ventilation to theworking places; (2) a preliminary treatment of thewater used for spraying and washing down; and(3) perhaps the use of exhaust-hoods (Sheffield hoodprinciple) in certain circumstances. There is evidencethat " tube-trouble "-the machine water-tubes-may be responsible for intermittent exposure torelatively dense clouds of dust ; it is considered thatsuch intermittent exposure is the deciding factor inproducing the disease in susceptible human subjects.The returns show that about 70 per cent. of thesilicotic cases occur in men who have used machinedrills at some time or other, although such men onlyamount to about 30 percent. of the men employedunderground at any one time. It seems reasonablethen to suspect the machine-drills, and further researchis planned to elucidate such problems.

THE INFLUENCE OF THE OVARY ONPITUITARY SECRETION.

RECENT researches on the condition known as

pseudo-pregnancy have a direct bearing on theproblem as to the cause of parturition. In the dog,rabbit, and some other animals the corpus luteumpersists during pseudo-pregnancy in the same kind ofway as it does during true pregnancy, and the uterusand mammary glands undergo growth in correlationwith the growth of the corpus luteum. In the rabbit,which normally only ovulates after coition, thecondition of pseudo-pregnancy can be induced bypermitting the doe to have a sterile coition (as with avasectomised buck). The corpus luteum after beingapparently functionally active eventually undergoesinvolution, and in association with this process theuterus also regresses and the mammary glands beginto secrete milk. There is no clear evidence that theovary has any direct influence in bringing aboutparturition.

In the current number of the Journal of PhysiologyW. E. Dixon and F. H. A. Marshall describefour experiments in which extracts of wholeovaries of rabbit and sow were employed, and theprecise stage of pregnancy or of the oestrous cyclenoted at which the animals were killed. Boiled Ringerextract of ovaries-rabbit and sow-was injectedinto the vein in dogs, the cerebro-spinal fluid collectedat suitable intervals, and its effect on the uterus ofa virgin guinea-pig tested in the usual way. Dixon