198 TEXT-BOOK OF BACTERIOLOGY. 



regularly present in that affection; when, further, it can be culti- 

 vated outside the organism; and when, lastly, it is able to reproduce 

 the same pathological effects when its artificial cultures are inocu- 

 lated. There are, it is true, but few bacteria that are in the happy 

 position to fulfil all these requirements. With one species this link, 

 with another that link, is wanting in the chain of irrefragable proof; 

 but it has already been stated that, supported by other experiences 

 and known facts, we at the present day are in some cases justified 

 in calling a certainty that which, properly speaking, is only a very 

 high degree of probability. 



As to the order in which we take up the different pathogenic 

 species, it will be an advantage if we bring together some smaller 

 groups whose members offer certain points of resemblance and 

 can be regarded from a common point of view. The order of the 

 members within such a group is a matter of indifference. 



I. ANTHRAX BACILLUS. 



Anthrax is one of the most widely- spread and most destructive 

 diseases which attack cattle of all kinds, and it is not infrequently 

 communicated from them to mankind. In its appearance and prog- 

 ress it offers so many peculiarities that investigators long since 

 turned their attention to it and sought to discover its exciting 

 causes. The discovery of the anthrax bacillus was the first step 

 into a world till then almost unknown. 



In 1849 Pollender saw rod-like forms in the blood of cattle af- 

 fected with anthrax, and shortly afterward Brauell, quite indepen- 

 dent of the first-named examiner, noticed the same thing. Both 

 recognized the vegetable nature of these forms, perceived that they 

 were foreign to the animal body, but both failed to comprehend 

 their true importance. 



It is to Davaine, who published his celebrated observations in 

 1863, that the most credit is due for the elucidation of this subject. 

 He was the first to assert definitely that the rod-cells were the cause 

 of the disease, and if not able to prove the truth of his assertion, 

 at least to make it extremely probable by a series of admirable 

 investigations. He showed that the bacteria are a constant accom- 

 paniment of anthrax, and completed his discovery by a very con- 

 vincing experiment, which had been tried in a similar manner by 

 Brauell before him. If he inoculated healthy animals with the 

 blood of sheep affected with anthrax after the bacteria had been 

 separated from it, they bore it without any injury; but they per- 

 ished without exception when the inoculated blood contained the 



