20 REPORT—1896. 
infallibly caused rabies in that animal in a few days. If therefore such 
an experiment was made with a negative result, the conclusion might 
be drawn with certainty that the dog had been healthy. It is perhaps 
right that I should say that the inoculation is painlessly done under an 
anesthetic, and that in the rabbit rabies does not assume the violent form 
that it does in the dog, but produces gradual loss of power with little if 
any suffering. — 
This is the more satisfactory because rabbits in which the disease has 
been thus artificially induced are employed in carrying out what was 
Pasteur’s greatest triumph, the preventive treatment of Hydrophobia in 
the human subject. We have seen that Pasteur discovered that microbes 
might under some circumstances undergo mitigation of their virulence. 
He afterwards found that under different conditions they might have it 
exalted, or, as he expressed it, there might be a renforcement du virus. 
Such proved to be the case with rabies in the rabbit ; so that the spinal 
cords of animals which had died of it contained the poison in a highly 
intensified condition. But he also found that if such a highly virulent 
cord was suspended under strict antiseptic precautions in a dry atmosphere 
at a certain temperature, it gradually from day to day lost in potency, till 
in course of time it became absolutely inert. If now an emulsion of such 
a harmless cord was introduced under the skin of an animal, as in the 
subcutaneous administration of morphia, it might be followed without harm 
another day by a similar dose of a cord still rather poisonous ; and so from 
day to day stronger and stronger injections might be used, the system 
becoming gradually accustomed to the poison, till a degree of virulence 
had been reached far exceeding that of the bite of a mad dog. When this 
had been attained, the animal proved incapable of taking the disease in 
the ordinary way ; and more than that, if such treatment was adopted 
after an animal had already received the poison, provided that too long a 
time had not elapsed, the outbreak of the disease was prevented. It was 
only after great searching of heart that Pasteur, after consultation with 
some trusted medical friends, ventured upon trying this practice upon 
man. It has since been extensively adopted in various parts of the world 
with increasing success as the details of the method were improved. It is 
not of course the case that every one bitten by a really rabid animal takes 
the disease ; but the percentage of those who do so, which was formerly 
large, has been reduced almost to zero by this treatment, if not too long 
delayed. 
While the intensity of rabies in the rabbit is undoubtedly due toa 
peculiarly virulent form of the microbe concerned, we cannot suppose that 
the daily diminishing potency of the cord suspended in dry warm air is 
an instance of attenuation of virus, using the term ‘ virus’ as synonymous 
with the microbe concerned. In other words, we have no reason to 
believe that the special micro-organism of hydrophobia continues to 
develop in the dead cord and produce successively a milder and milder 
