The President's Address. By G. S. Woodhead. 121 



experiment.* Taking fluid, diluted blood, in which the presence of 

 the anthrax bacillus could be demonstrated by means of the 

 Microscope and by experiments upon animals, he filtered it 

 through earthenware, and found that, although the part kept back 

 by the filter contained the bacilli, and was still capable of pro- 

 ducing the disease, the filtrate, in which no bacilli could be 

 found, was absolutely innocuous. It was left to Koch, however, 

 to lay down the lines of research in connexion with the demon- 

 stration of the etiology of most of the infective diseases now 

 recognized. By means of admirable technique he succeeded in 

 studying the anthrax bacillus in great microscopical detail.f After 

 demonstrating its presence in the blood' of animals dying from 

 anthrax, he succeeded, by the use of solidifying media — which 

 had first been used by Klebs, whose work Koch seems to have 

 studied with keen appreciation — in isolating and cultivating 

 colonies arising from individual bacteria, colonies that could be 

 watched under the Microscope as they grew,' and their various 

 phases of development noted. From these individual colonies 

 pure cultures were obtained, and by transferring the organism from 

 one lot of medium to another all possibility of anything but the 

 growing organisms remaining was removed. With the organisms 

 so separated and purified, organisms that had the same micro- 

 scopical character as had those found in the blood of the original 

 diseased animal, he produced definite anthrax by inoculating them 

 into various animals ; from these animals he isolated the original 

 organism, with which he succeeded in repeating the whole series 

 of experiments. Further, he showed that when the organism was 

 allowed to grow outside the body under special conditions — con- 

 ditions apparently unfavourable to the continuance of the species 

 — it had the power of forming spores, bodies that he had never 

 met with in the organism as it occurred in the fresh blood of 

 animals dying from the disease, but which were afterwards found 

 in old shed blood, i.e. when the bacillus came into contact with 

 the air. He noted the resistance of these spores, and recognized 

 their importance in maintaining the continuity of the species 

 outside the animal body. He and his pupils now put to the 

 test many of the observations that had been made by his brilliant 

 predecessors, Henle and Edwin Klebs, observations on miasmata 

 and contagia and on wound-infection that constituted epoch- 

 making contributions to our knowledge of these conditions. 

 He applied his methods to the bacteria of no fewer than six 

 "infections," and showed that each bred true, each produced a 

 definite form of disease, and that five at least could be again 

 isolated and cultivated from the inoculated experimental animals. 

 Such revolutionary methods and observations were naturally 



* Cor.-Bl. f. Schweiz. Aerzte, Bern, i. (1871) p. 279. 

 t Die Aetiologie der Milzbrand Kraukheit, 1876. 



