1885.] on Living Contagia. 165 



close to the prohibitary temperature. Now the bloorl-corpuscles of a 

 living fowl are sure to offer a certain resistance to any attempt to 

 deprive them of tlitir oxygen. But close to its prohibitory tempera- 

 ture, the anthrax ctntagiiim may be expected to be enfeebled, and the 

 question arises : May not the blood-corpuscles in those circumstances 

 be ahle successfully to combat the organism? Experiment al(»ne 

 could decide, and Pasteur made the experiment. He lowered, by 

 chilling in cold water, the temperature of a fowl 4P \ and while in 

 this condition inoculated it with the splenic fever parasite. In 

 twenty-four hours the fowl was dead. Inoculating another fowl 

 similarly chilled, he permitted the fever to come to a head, and then 

 transferred the fowl to a warm chnmber. The career of the parasite 

 was soon stopped, and in a few hours the health of the fowl was 

 restored. Tlie issues of this experiment, as suggesting the application 

 of heat or cold in the fevers which afflict humanity, are incalculable. 



Pasteur next attacked the fatal malady of chicken cholera. The 

 parasite of this disease had been discovered before him ; but, by a 

 method now universally applied, he rendered the solution of the 

 problem sure. Into chicken broth, boiled sufficiently long to destroy 

 all germs with which it may be contaminated, let a minute drop of 

 the blood of a fowl suffering from chicken cholera be introduced. 

 The organisms of the bluod increase and multiply, until they finally 

 invade the whole of the nutritive liquid. With the point of a needle, 

 let a speck of this liquid be introduced into a second sterilised 

 infusion. As before, the organisms multiply until the liquid becomes 

 thick with them. Let a speck, taken on the needle-point from this 

 second cultivation, be communicated to a third sterilised infusion. 

 A similar result will be observed. In this way any number of 

 generations of the organism may be cultivated, and whatever foreign 

 matter, chemical poison, or otherwise, might attach itself to the drop 

 of blood first taken from the animal, is thus washed away. This is 

 the method oi " pure culture" now pursued. After fifty cultures, let 

 a speck of the infected infusion be introduced into the blood of a 

 healthy fowl. Cholera and death are the consequence. The organism 

 is as virulent as at first. But here we come to a point of supreme 

 importance. The virulence is maintained on one condition. The 

 cultures must rapidly succeed each other. When the infusion with 

 its swarming organisms is allowed to remain for a week, for a 

 fortnight, fur a month, for two months, without renewal, the power of 

 the organism gradually diminishes, and after a certain time, though 

 it may be able to produce malaise, it is not able to produce death. It 

 thus becomes what Pasteur calls an attenuated virus — a true vaccine. 

 For, if with the organism in this condition, a fowl be inoculated, the 

 subsequent malaise passes away, and the fowl is afterwards proof 

 against the organism in its most virulent form. 



Pasteur next laid hold of the murderous virus of splenic fever, 

 and succeeded in rendering it not only harmless to life, but a sure 

 protection against the assaults of the disease. It was soon noised 



