MODE OF SPREAD IN NATURE. 291 



open up a way for our arriving at an idea of the true 

 pathology of the disease. The bacilli in all parts of the 

 body, whether directly or intermediately by ferments, pro- 

 duce bodies toxic to tissue cells. Further, bacilli confined 

 locally produce by this means effects on distant tissues. 

 This explains how in certain cases, while the bacilli are 

 still locally confined, there may occur cedema spreading 

 from the pustule, and pyrexia. 



The Spread of the Disease in Nature. If we take the 

 case of an animal suffering from anthrax, we have to ask 

 how it communicates the disease to others. We have seen 

 that the B. anthracis rarely, if ever, forms spores in the body, 

 and if the bacilli could be confined to the blood and tissues 

 of the carcase, it is certain that anthrax in an epidemic form 

 would rarely occur. For it has been shown by many ob- 

 servers that in the course of the putrefaction of such a 

 carcase the anthrax bacilli rapidly die out, and that after 

 ten days or a fortnight very few remain. But it must be 

 remembered that while still alive, an animal is shedding into 

 the air by the bloody excretions from the mouth, nose, and 

 bowel, myriads of bacilli which may rapidly spore, and thus 

 arrive at a very resistant stage. These lie on the surface 

 of the ground and are washed off by surface water. At 

 certain seasons of the year the temperature is, however, 

 sufficiently high to permit of their germination, and also of 

 their multiplication, as they can undoubtedly grow on the 

 organic matter which occurs in nature. They can again 

 form spores. It is in the condition of spores that they are 

 dangerous to susceptible animals. In the bacillary stage, if 

 swallowed, they will be killed by the acid gastric contents ; 

 but as spores they can pass uninjured through the stomach, 

 and, gaining an entrance into the intestine, infect its wall, 

 and ultimately reach, and multiply in, the blood. It was 

 thought by some, including Pasteur, that infection took 

 place by bacilli infecting excoriations about the mouth and 

 fauces ; and the occasional occurrence of great lymphatic 

 enlargement in the cervical region was adduced in support 

 of this view. It was also supported by the want of success 



