332 ANTHRAX 



causal connection with the disease. In 1863 Davaine announced that 

 they were bacteria, and originated the name bacillus anthracis. He stated 

 that unless blood used in inoculation experiments on animals contained 

 them, death did not ensue. Though this conclusion was disputed, still 

 by the work of Davaine and others the causal relationship of the bacilli 

 to the disease had been nearly established when the work of Koch 

 appeared in 1876. This constituted that observer's first contribution to 

 bacteriology, and did much to clear up the whole subject. Koch con- 

 firmed Davaine's view that the bodies were bacteria. He observed in the 

 blood of anthrax animals the appearance of division, and from this 

 deduced that multiplication took place in the tissues. He observed them 

 under the microscope dividing outside the body, and noticed spore forma- 

 tion taking place. He also isolated the bacilli in pure culture outside 

 the body, and, by inoculating animals with them, produced the disease 

 artificially. In his earlier experiments he failed to produce death by 

 feeding susceptible animals both with bacilli and spores, and as the 

 intestinal tract was, in his view, the natural path of infection, he con- 

 sidered as incomplete the proof of this method of the spontaneous occur- 

 rence of anthrax in herds of animals. Koch's observations were, shortly 

 afterwards, confirmed in the main by Pasteur, though controversy arose 

 between them on certain minor points. Moreover, further research 

 showed that the disease could be produced in animals by feeding them 

 with spores, and thus the way in which the disease might spread 

 naturally was explained. 



Bacillus Anthracis. Anthrax as a disease in man is of 

 comparative rarity. Not only, however, is the bacillus 

 anthracis easy of growth and recognition, but in its growth it 

 illustrates many of the general morphological characters of the 

 whole group of bacilli, and is therefore of the greatest use to the 

 student. Further, its behaviour when inoculated in animals 

 illustrates many of the points raised in connection with the 

 general pathogenic effects of bacteria, immunity, etc. Hence 

 an enormous amount of work has been done in investigating it 

 in all its aspects. 



If a drop of blood is taken immediately after death from an 

 auricular vein of a cow, for example, which has died from 

 anthrax, and examined microscopically, it will be found to con- 

 tain a great number of large non-motile bacilli. On making 

 a cover-glass preparation from the same source, and staining with 

 watery methylene-blue, the characters of the bacilli can be better 

 made out. They are about 1'2 //, thick or a little thicker, and 

 6 to 8 //, long, though both shorter and longer forms also occur. 

 The ends are sharply cut across, or may be slightly dimpled so 

 as to resemble somewhat the proximal end of a phalanx. Their 

 protoplasm is very finely granular, and very frequently appears 

 surrounded by a capsule whose external margin is not, however, 

 so well defined as is the case with, e.g., the pneumococcus. When 

 several bacilli lie end to end in a thread, the capsule seems 



