I 
8 KOBEKT MEADE SMITH. 
but aims in the dark, treating symptoms as they arise while the 
true causus morbi escape us. This will be abundantly proved 
when we come to consider the results of the experimental produc¬ 
tion of the various morbid states. Those which we are able to pro¬ 
duce at will, we will find, will be those in which our success in 
prevention and cure is the most marked ; while those which have 
still eluded all attempts at the isolation of their specific virus are 
those in which we are most helpless. 
The most important discovery that has ever been made in 
pathology was the recognition of minute vegetable or animal 
organisms as the cause of different contagious diseases; and how 
could that discovery be made but through experiments on animals. 
It had long been known that the blood and secretions of men and 
animals suffering from the different contagious diseases were 
crowded with these organisms (bacilli), but until we were able, 
by isolating these bacilli and injecting them into the blood of 
other animals to produce the same disease, we could not be sure 
that they were actually the cause of the disease, and not mere 
coincidences; or that they flourished in the blood of such dis¬ 
eased subjects, because that fluid had undergone some subtle 
change, absent in normal blood, and favorable to the vital condi¬ 
tions of those organisms. 
But that is not all. Great discovery as it was to be able to 
isolate the agent of these deadly diseases, it was still more won¬ 
derful that in the study of the characters of those organisms we 
should be able to discover the means by which we could not only 
rob them of their deadly attributes, but that we could make these 
organisms themselves serve to prevent the very disease it is their 
nature to produce. And how could this be determined but by 
experiments on animals? It was found that by cultivating these 
organisms in proper nutritive fluids, or by subjecting them to 
definite degrees of heat, they gradually lost their virulence and 
even acquired the property of preventing disease. 
Many experiments were necessary to establish this. Numer¬ 
ous experiments, entailing the death or disease of the animal ex¬ 
perimented on, had first to be made to prove that the actual cause 
of the disease had been isolated. Other experiments were then 
