420 



SCIENCE. 



[N. S. Vol. IV. No. 91. 



their many acliievements is what may be 

 fairly regarded as the most important dis- 

 covery ever made in pathology, because it 

 revealed the true nature of the disease 

 which causes more sickness and death in • 

 the human race than any other. It was 

 made by Eobert Koch, who greatly distin- 

 guished himself, when a practitioner in an 

 obscure town in Germany, by the remark- 

 able combination of experimental acuteness 

 and skill, chemical and optical knowledge 

 and successful micro-photography which he 

 brought to bear upon the illustration of in- 

 fective diseases of wounds in the lower ani- 

 mals ; in recognition of which service the 

 enlightened Prussian government at once 

 appointed him to an official position of 

 great importance in Berlin. There he con- 

 ducted various important researches; and 

 at the London Congress, in 1881, he showed 

 to us, for the first time, the bacillus of 

 tubercle. Wonderful light was thrown, by 

 this discovery, upon a great group of dis- 

 eases which had before been rather guessed 

 than known to be of an allied nature; a 

 precision and efficacy never before possible 

 was introduced into their surgical treat- 

 ment, while the physician became guided 

 by new and sure light as regards their 

 diagnosis and prevention. 



At that same London Congress Koch 

 demonstrated to us his ' plate culture ' of 

 bacteria, which was so important that I 

 must devote a few words to its description. 

 With a view to the successful study of 

 the habits and effects of any particular 

 microbe outside the living body it is 

 essential that it should be present unmixed 

 in the medium in which it is cultivated. It 

 can be readily understood how difficult it 

 must have been to isolate any particular 

 micro-organism when it existed mixed, as 

 was often the case, with a multitude of 

 other forms. In fact, the various ingenious 

 attempts made to effect this object had 

 often proved entire failures. Koch, how- 



ever, by an ingenious procedure converted 

 what had been before impossible into a 

 matter of the utmost facility. In the broth 

 or other nutrient liquid which was to serve 

 as food for the growing microbe he dis- 

 solved, by aid of heat, just enough gelatine 

 to ensure that, while it should become a 

 solid mass when cold, it should remain fluid, 

 though reduced in temperature so much as 

 to be incapable of killing living germs. To 

 the medium thus partially cooled was added 

 some liquid containing, among others, the 

 microbe to be investigated; and the mix- 

 ture was thoroughly shaken so as to diffiise 

 the bacteria and separate them from each 

 other. Some of the liquid was then poured 

 out in a thin layer upon a glass plate and 

 allowed to cool so as to assume the solid 

 form. The various microbes, fixed in the 

 gelatine and so prevented from interming- 

 ling, proceeded to develop each its special 

 progeny, which in course of time showed 

 itself as an opaque speck in the transparent 

 film. Any one of such specks could now 

 be removed and transferred to another ves- 

 sel in which the microbe composing it grew 

 in perfect isolation. 



Pasteur was present at this demonstra- 

 tion, and expressed his sense of the great 

 progress effected by the new method. It 

 was soon introduced into his own institute 

 and other laboratories throughout the world; 

 and it has immensely facilitated bacterio- 

 logical study. 



One fruit of it in Koch's own hands was 

 the discovery of the microbe of cholera in 

 India, whither he went to study the disease. 

 This organism was termed by Koch from 

 its curved form the ' comma bacillus,' and 

 by the French the cholera vibrio. Great 

 doubts were for a long time felt regarding 

 this discovery. Several other kinds of bac- 

 teria were found of the same shape, some 

 of them producing very similar appearances 

 in culture media. But bacteriologists are 

 now universally agreed that, although va- 



