NA TURE 



THURSDAY, MARCH 27, lE 



THE CHOLERA BACILLUS 



IN his capacity as chief of the German Cholera Com- 

 mission Dr. Koch has issued a further — his sixth — 

 report, and it is one which must become historic in con- 

 nection with inquiries as to the etiology of that disease. 

 Hitherto Dr. Koch has almost entirely confined himself 

 to reporting facts as they were elicited, and whenever he 

 has referred to any inferences which might be drawn 

 from them, it has only been to show how many sources 

 of error stood in the way of all attempts to arrive at 

 trustworthy conclusions. This attitude of Dr. Koch has 

 naturally tended to increase the confidence in which 

 he is held as a scientific worker, and it has an important 

 bearing on the character of the present report, in which 

 the reserve hitherto maintained is thrown off, and Dr. 

 Koch announces that the bacilli he has discovered are 

 altogether peculiar to cholera, and further, that they are 

 the actual cause of cholera. 



The further investigations which have been made relate 

 to the cultivation of the bacilli in question, to their be- 

 haviour in the bodies of patients during the various 

 stages of the disease, and to the examination of addi- 

 tional bodies of persons dying both of cholera and of 

 other diseases. The result is that what are now termed 

 the cholera bacilli can be found in no bodies except those 

 of cholera patients ; that at certain stages of the cholera 

 disease they are invariably found in the bodies of the 

 patients, whether these have lived and died in Egypt or 

 in a country so far distant from it as India ; that these 

 organisms confine themselves to the organ which is the seat 

 of the disease, namely, the bowel ; and that they behave 

 exactly as do other pathogenic bacteria, their first appear- 

 ance coinciding with the commencement of the disease, 

 their increase bein^; proportional to its advance, and their 

 disappearance corresponding with its decline. Certain 

 incidental studies have also tended to confirm the correct- 

 ness of the hypothesis that these bacilli are the cause of 

 cholera. It is well known that the linen of cholera 

 patients, has conveyed the infection of that disease. Now 

 Dr. Koch has repeatedly observed that such linen, when 

 soiled by the alvine discharges and kept moist for a 

 period of twenty-four hours, has been the seat of an 

 extraordinary multiplication of the special organisms ; 

 and in connection with these experiments it was found 

 that precisely the same result took place whenever cholera 

 dejections, or the contents of the intestines of persons 

 having died of cholera, were spread upon such substances 

 as moist linen or blotting paper. And further, a thin 

 layer of the same discharges, when placed on a moist 

 soil, was found within twenty-four hours to have been 

 converted into a thick mass of cholera bacilli. This latter 

 discovery is one of extreme importance in connection 

 with the observations so frequently made as to the spread 

 of cholera in India by means of water-sources, the soil 

 around which is so often befouled by the natives. 



From one point of view the report gives special 

 promise. Some bacilli of disease will, in certain stages, 

 withstand almost every form of maltreatment ; they may 

 Vol. XXIX. — No. 752 



497 



J 



be dried, frozen, and- otherwise dealt with, and yet they 

 'remain as potent as ever for mischief. But Dr. Koch's 

 cholera bacilli die off rapidly when dried, all vestige of life 

 apparently disappearing after three hours' desiccation. 

 And not only so, but these bacilli will only grow in alka- 

 line solutions, a very small quantity of a free acid standing 

 in the way of their development. To these two circum- 

 stances we may in all probability to a large extent attri- 

 bute the frequency with which those who are directly 

 associated with the sick and their discharges escape in- 

 fection ; and the fact that the healthy stomach contains a 

 sufficient amount of acid to destroy the bacilli may 

 possibly lead to the discovery of some therapeutic or 

 other measure of prevention which may be generally 

 adopted. Directly gastric disturbance steps in and the 

 gastric juices give a different reaction, we are probably 

 face to face with conditions specially favourable to the 

 . reception of the poison, and in this respect it is note- 

 'worthy that cholera so often attacks those persons who 

 have suffered, or are suffering, from diarrhosa and other 

 gastric disorders. 



In one respect Dr. Koch's experiments have failed. He 

 has not succeeded in producing cholera artificially in any 

 of the lower animals. As we have already pointed out, 

 cholera is not the only specific disease to which man 

 alone appears to be susceptible ; and it is possible that 

 the fact of cholera discharges and portions of diseased 

 intestines having been given as food to the lower animals 

 with impunity may find much of its explanation in the 

 absence, in the stomachs of those animals, of the needed 

 alkaline cultivation fluid. 



At one point of the report our confidence in the correct- 

 ness of Dr. Koch's inferences is weakened. It is where 

 he, in maintaining his view that the bacillus he has dis- 

 covered is the actual cause of cholera, refers to its 

 resemblance in one respect to the bacillus of enteric 

 fever. Now, leading micro-pathologists in this country 

 have hitherto declined to regard it as proved that any 

 such specific bacillus has been discovered. Dr. Koch's 

 views have therefore still to stand the test of scientific 

 .criticism by his fellow workers, who will doubtless, as 

 occasion oft'ers, repeat his experiments. 



THE SCIENCE OF THE EXAMINA T ION-ROOM 

 'H^HOSE persons whose unhappy lot it is to have much 

 -L to do with examinations must often feel that there 

 is some fundamental common factor dropped out in the 

 relation between examiner and examinees. A straight- 

 forward paper is set in a subject, say A, in which we will 

 suppose there is no attempt to " catch " or perplex the 

 student, but simply to sample, as it were, the ordinary 

 commonplace knowledge which average industry might 

 acquire. There returns to the examiner in due time a 

 mass of manuscript, evidently written with pains and 

 labour, mostly quite seriously meant, but which does not 

 deal with the subject A, but with something which, though 

 apparently related, is evidently quite different, and which 

 we may call A'. After a little while he begins to wonder 

 whether the whole thing is not a nightmare. 1 he form 

 is apparently rational, and yet the details are hopelessly 

 incongruous and absurd. Or, to put the thing in another 

 shape, it is as if one set a paper in solid geometry and 



