64 PASTEUR AND AFTER PASTEUR 



where he stood, even before 1880. He and his 

 pupils could isolate the germs of this or that 

 disease ; could grow them in pure culture, in a 

 test-tube, miles away from a patient ; could repro- 

 duce the disease, with a drop of this pure culture, 

 in a rabbit or a guinea-pig. We are so familiar, 

 by this time, with stacks of culture-tubes, that we 

 are apt to forget what a miracle it was, and is, to 

 be able thus to bottle a disease. To have, in one's 

 hands, outside the living body, cholera or plague 

 or Malta fever or typhoid or diphtheria the wonder 

 of it, the sense of seeing, with our own eyes, the 

 real cause, the very stuff, the thing itself, growing 

 in a test-tube we take it for granted nowadays. 

 Only, from time to time, one more disease is 

 brought within the range of this method, and the 

 wonder is renewed, as we hold in our hands, in 

 a test-tube, syphilis, or epidemic meningitis. Then, 

 in 1880, Pasteur advanced, from the making of 

 cultures, to the attenuation of cultures : and to 

 the supreme discovery, that an attenuated culture 

 is able to confer immunity against a culture at 

 full strength. 



A pure culture of the germs of chicken- cholera, 

 he found, lost strength, slowly and steadily, from 

 day to day, by mere keeping. Thus, he could 

 prepare and stock a graduated series of cultures, 

 in every shade of strength, from full virulence to 



