666 APPENDIX. 
had actually been bitten by a rabid, or presumably 
rabid, animal, Pasteur continued bis experiments, in 
order to see whether it would not be possible to cure a 
patient already bitten. He carried on, therefore, a 
series of experiments which led to the discovery that if 
the process of inoculation be begun within five days of 
the bite in animals in which the incubation period was 
at least fourteen days, almost every animal bitten can 
be saved; and that even if the treatment be com- 
menced at a longer interval after the bite a certain 
proportion of recoveries can be obtained. Thus the 
application of this method of treatment to the human 
subject was not tried until it had been proved in 
animals that such protection could be obtained, and 
that such protection would last for at least two years, 
and probably longer. 
The chance of success in the human subject appears 
to be even greater than in the dog or rabbit, seeing that 
on account of the resistance offered by the human tissues 
to the virus the period of incubation is comparatively 
prolonged; very rarely, if ever, does an outbreak of the 
disease in man occur before an interval of at least fifteen 
days. The first symptoms usually appear in the fifth 
or sixth week, sometimes not until the third month ; 
exceptionally the incubation period has lasted for a 
year. Thus there is an opportunity of obtaining 
immunity by beginning the process of vaccination 
soon after the bite has been inflicted, the protection 
being complete before the incubation period has passed. 
In his earlier experiments Pasteur injected on each 
succeeding day emulsions from a cord dried for one 
_ day less until cords dried five days were reached; but 
later he used those dried for only three days. This 
