132 
M. L. PASTEUR. 
inquiry of interest to know whether the immunity referred to eun 
be absolute, not only respecting the regions of the body which 
have received the preventive inoculation, but also what should be 
the point selected for the operation, and as well, the mode of in¬ 
troduction of the disease and the degree of receptivity in the 
animal chosen for the experiment.* 
To explain more clearly and more briefly the results I wish to 
relate, allow me to use the word vaccinate in referring to the in¬ 
oculation of the chicken with attenuated virus. This admitted, I 
may say, on the faith of many experiments, that the effects of 
vaccination vary with chickens ; that some resist a very active 
virus after one preventive inoculation of weak virus; that others 
need two and even three preventive inoculations ; that in all cases, 
in fact, any preventive inoculation has its own proper action, and 
it always protects in a certain measure ; that, in a word, though 
there will always be degrees of effectiveness, it is always possible 
to accomplish a successful vaccination—that is, to bring the 
chicken to a condition where the most active virus will cease to 
be effective. 
A brief recital of the methods and results of the experiments 
which furnished the demonstration of my views, will render their 
statements more intelligible : 
I take eighty fresh hens—I call them fresh because they never 
had the disease either spontaneously or in any other way. Of 
these I inoculate twenty with the lymph of the most virulent 
character, and all die. From the sixty remaining, I inoculate 
*What I have heard or read of human vaccine, and what I may infer from 
my own experiments on chicken cholera, induce me to believe that vaccination 
seldom produces its maximum effect. Indeed, where is the vaccinator who would 
without apprehension expose his vaccinated patients to a fatal epidemic of vari¬ 
ola ? Reports exist of vaccinated persons who had previously had variola, and 
in whom vaccination proved afterwards efficacious, who subsequently suffered 
attacks of variola and had had this disease three times. Dr. Brouardel reports: 
Mrs. C. D. vaccinated in her youth; came to Passy when 30 years old. Her face 
was pitted from variola, when at 20 or 22 years. In 1868 she was treated for 
another attack of confluent small-pox. She came to Paris in 1869; was success¬ 
fully vaccinated in 1870, and in 1874 had another attack of varioloid—-presenting 
the phenomenon in the same person of two attacks of vaccination and three of 
variola, of which two were of the confluent variety. 
