PASTEUR'S RESEARCHES IN GERM-LIFE. 93 



multiplication of bacillus anthracis in infusions is 44 C. (111 Fahr.). 

 The temperature of the blood of birds is from 41 to 42 Fahr. 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 tempera- 

 ture of a fowl to 37 or 38 Fahr. He inoculated the fowl, thus chilled, 

 with the splenic-fever parasite, and in twenty-four hours it was dead. 

 The argument was clinched by inoculating a chilled fowl, permitting 

 the fever to come to a head, and then removing the fowl, wrapped 

 in cotton-wool, to a chamber with a temperature of 35 Fahr. The 

 strength of the patient returned as the career of the parasite was 

 brought to an end, and in a few hours health was restored. The 

 sharpness of the reasoning here is only equaled by the conclusiveness 

 of the experiment, which is full of suggestiveness as regards the treat 

 ment of fevers in man. 



Pasteur had little difficulty in establishing the parasitic origin of 

 fowl-cholera ; indeed, the parasite had been observed by others before 

 him. But, by his successive cultivations, he rendered the solution sure. 

 His next step will remain forever memorable in the history of medicine. 

 I allude to what he calls " virus attenuation." And here it may be well 

 to throw out a few remarks in advance. When a tree, or a bundle of 

 wheat or barley straw, is burned, a certain amount of mineral matter re- 

 mains in the ashes extremely small in comparison with the bulk of the 

 tree or of the straw, but absolutely essential to its growth. In a soil 

 lacking, or exhausted of, the necessary mineral constituents, the tree 

 can not live, the crop can not grow. Now, contagia are living things, 

 which demand certain elements of life just as inexorably as trees, or 

 wheat, or barley ; and it is not difficult to see that a crop of a given 

 parasite may so far use up a constituent existing in small quantities in 

 the body, but essential to the growth of the parasite, as to render the 

 body unfit for the production of a second crop. The soil is exhausted, 

 and, until the lost constituent is restored, the body is protected from 

 any further attack of the same disorder. Such an explanation of non- 

 recurrent diseases naturally presents itself to a thorough believer in 

 the germ theory, and such was the solution which, in reply to a ques- 

 tion, I ventured to offer nearly fifteen years ago to an eminent London 

 physician. To exhaust a soil, however, a parasite less vigorous and 

 destructive than the really virulent one may suffice ; and, if, after hav- 

 ing by means of a feebler organism exhausted the soil, without fatal 

 result, the most highly virulent parasite be introduced into the system, 

 it will prove powerless. This, in the language of the germ theory, is 

 the whole secret of vaccination. 



