XXXIV INTRODUCTION. 



introduced by me in February 1877 was founded. The 

 difference between an organism and its spores, in point 

 of durability, had not escaped the penetration of 

 Pasteur. This difference Koch showed to be of para- 

 mount importance in splenic fever. He, moreover, 

 proved that while mice and guinea-pigs were infallibly 

 killed by the parasite, birds were able to defy it. 



And here we come upon what may be called a hand- 

 specimen of the genius of Pasteur, which strikingly 

 illustrates its quality. Why should birds enjoy the 

 immunity established by the experiments of Koch ? 

 Here is the answer. The temperature which prohibits 

 the multiplication of bacillus anthracis in infusions is 

 44 Cent. (111 Fahr.). The temperature of the blood 

 of birds is from 41 to 42. It is therefore close to 

 the prohibitory temperature. But then the blood 

 globules of a living fowl are sure to offer a certain 

 resistance to any attempt to deprive them of their 

 oxygen a resistance not experienced in an infusion. 

 May not this resistance, added to the high tempera- 

 ture of the fowl, suffice to place it beyond the power 

 of the parasite? Experiment alone could answer 

 this question, and Pasteur made the experiment. 

 By placing its feet in cold water he lowered the tem- 

 perature of a fowl to 87 or 38. He inoculated 

 the fowl, thus chilled, with the splenic fever parasite, 

 and in twenty- four hours it was dead. The argu- 

 ment was clinched by inoculating a chilled fowl, per- 



