ZOOLOGICAL DISTRIBUTION OF DISEASE. 253 



Anthrax demonstrates in a remarkable manner why 

 disease should have a zoological distribution, for slight 

 physiological differences protect an animal against the 

 action of the anthrax bacillus, the morbific agent of the 

 ruinous splenic fever. This disease can easily be com- 

 municated to the ox, sheep, rabbit, and guinea pig by 

 injecting into the circulation a small quantity of blood 

 taken from an animal which has died of splenic fever. 

 Such injections are rapidly fatal. On the other hand, it 

 is difficult to inoculate the dog and pig, and fowls never 

 acquire the disease. The cause of the immunity of 

 fowls has been cleverly explained by Pasteur. It had 

 been ascertained that the anthrax bacillus does not 

 develop when subjected to a temperature of 44 Centi- 

 grade. The body temperature of a fowl is about 41 C., 

 whilst that of the horse is 37*7 C., the dog and 

 rabbit, 38-39 C. On immersing the feet of a fowl in 

 cold water at a temperature of 25 Cent, so as to 

 reduce its body heat to 37 or 38, and then injecting 

 it with blood from a case of splenic fever, it was 

 found at the end of twenty-four hours dead, with its 

 blood filled with the bacteria of splenic fever. In another 

 experiment a hen was inoculated and subjected to the 

 cold-water treatment ; when the fever was at its height 

 the hen was taken out of the water, wrapped carefully 

 in cotton wool and placed in an oven at 35 C. In the 

 course of a few hours it was restored to health. Hens 

 killed after being experimented upon in this way exhibit 

 no trace of the bacteria in their blood. 



Under ordinary conditions a frog cannot be killed by 

 injection of anthrax cultures, but if, after inoculating^ 



OF TH 



UNIVERSITY- 



