278 PASTEUR: THE HISTORY OF A MIND 



first culture has rendered the medium unsuitable for 

 a second, as the first attack of a virus disease protects 

 against all new attacks. Thus was sown in the mind 

 of Pasteur, a seed which fell on good ground and could 

 not fail to be productive. 



Inoculation with this organism is usually fatal but 

 it sometimes happens that the chicken, after having 

 been sick, seems to recover. Nevertheless it eats little, 

 its comb loses color, it grows thin, and finally it succumbs 

 after weeks or months of languor. Is it always the 

 same disease? Yes, for the organism which we find 

 in the tissues, if isolated, kills the chickens into which 

 it is inoculated. Why, then, did it not cause the death 

 of the chicken which carried it? Whence comes this 

 relative immunity? Pasteur was not yet able to 

 answer this question, but he already had the right to 

 put it to himself. While waiting to find the solution, 

 he pointed out the analogy between these larval forms 

 of the cholera, and the grave and often incurable forms 

 of certain virus diseases, such as measles, scarlatina, 

 and typhoid fever. 



Many ideas are already knocking at the portals of 

 his mind: and this is not the end. The chicken is not 

 the only domestic animal capable of offering a habitat 

 to the microbe. The dog, the horse, and many animals 

 of the barnyard are also inoculable. The rabbit is 

 particularly susceptible, and Pasteur discovered later 

 that the contagion could be propagated in terriers. 

 The guinea-pig, on the contrary, is quite resistant. 

 It succumbs to inoculations in the veins, but those 

 under the skin produce scarcely more than a slight abscess, 

 which bursts spontaneously and heals without making 

 the animal which bears it appear sick. This abscess 

 is a kind of pure culture of the microbe, and if we inocu- 

 late a little of its contents into chickens, " these chickens 



