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D. E. SALMON. 
tion of the standard virus and its dilution can be accomplished, 
with fowl cholera at least, within twenty-four hours from the 
time the particle of blood which originates it is taken from the 
affected animal. The stronger the virus the longer will it retain 
its full activity, and, hence, the unmitigated virus is in far the 
best condition for preservation, and the dilution can at any time 
be made in a few minutes. 
Again, the method of Pasteur cannot well be applied to 
human diseases, because it requires too many experiments to learn 
the degree of attenuation. In some cases the attenuation does 
not occur until a few hours before the death of the virus, while 
in other cases it may be weeks or months before. So that, in 
applying it to a new disease, there are no indications except 
those furnished by inoculation experiments. On the other hand, 
if we dilute we know that we attenuate. If we introduce but 
ten or twenty germs of almost any disease the probabilities are 
that the effect would be very slight; if such an inoculation were 
unsuccessful the number could be gradually increased. Surely 
when many people are exposed to a deadly plague, it would not 
be impossible to pursue this class of investigations. Of course, I 
only mean the above remarks to apply to those non-recurrent 
fevers from which immunity may be acquired within a few days 
or weeks. 
Whether I am right or wrong in considering that this method 
of preventive inoculation may, under certain circumstances, be 
used advantageously in controlling the plagues of mankind, it 
seems to me that the method by dilution has some incontestable 
advantages over the method of Pasteur. I may summarize these 
as follows : 1. The virus is obtained by a definite strength. 2. It 
may be preserved in the condition in which it retains its activity 
the longest time. 3. The attenuation requires but minutes in¬ 
stead of weeks or months. 4. The experiments to learn the 
proper degree of attenuation are less dangerous to the individuals 
operated upon. 5. These experiments once made, it is not neces¬ 
sary to repeat them with every fresh lot of virus. 6. One virus 
and one successful vaccination are all that is required. 7. The 
