DISCOVERY OF VACCINES 283 



there was this further resemblance that the absolute 

 conservation of the virulence was realized neither by the 

 vaccine transferred from arm to arm, as Jenner believed, 

 nor by the chicken cholera vaccine, transferred from 

 culture to culture, as Pasteur believed. In both cases, 

 there is a deterioration, but a very slow, one, which it 

 has required years to perceive. 



In any event, a new world was opened to him, and 

 he must push on into it eagerly. This is what Pasteur 

 did with the incomparable authority of a master, con- 

 stantly guided, it is true, by the then prevaihng notions 

 regarding virus diseases, but having as a means of illumi- 

 nating his every step those methods for cultivating 

 the virus which were entirely his own. I have no inten- 

 tion of following up his study of chicken cholera; I 

 should hke, merely, to point out the principal facts, 

 those which should not be forgotten because they tell 

 us, in a particularly simple case and one which has been 

 well worked out, what a virus disease really is. 



If we inject a few drops of a young culture of the 

 microbe of chicken cholera into one of the large pectoral 

 muscles of a chicken, or inject them into its blood, or 

 still better, put them on the food, on the bread or 'the 

 meat, we shall see, after a time varying with the path 

 of entrance, the symptoms of the disease appear in this 

 fowl. The animal loses its appetite, becomes drowsy, 

 ruffles itself into a ball and dies sometimes in 24 hours,' 

 entirely invaded by the microbe, which is found in its 

 blood and in all its organs. 



Instead of using a young culture for inoculation, let 

 us repeat the experiment with a culture several weeks 

 old. We shall still have a disease marked by loss of 

 appetite, drowsiness, and ruffled feathers, but the chicken 

 does not die. After some days of more or less severe 

 illness, it apparently fully recovers. There has been, 



