EXPERIMENTS ON ANIMALS. 
7 
ble in the treatment of similar diseases occurring as the result of 
natural causes; for it is the mystery which surrounds the origin 
of diseases which has always proved the most formidable obstacle 
to their cure. And, moreover, when diseases appears in a pre¬ 
viously healthy subject, the morbid process is never or rarely 
noticed until it has obtained a firm foothold on the system. The 
time has then passed, maybe, when our therapeutic interference 
can be of any avail. 
But when we produce a disease artificially the animal is kept 
under the closest observation, and the first trivial deviation from 
the state of health is noticed and may serve as the starting point 
of treatment which then has every prospect of success. Produc¬ 
tion of disease in animals bears the same relation to its diagnosis 
as synthesis does to analaysis in chemistry. We may analyze a 
chemical compound, but we can never be sure of its intimate con¬ 
struction until we are able to reform that compound by recombi¬ 
nation of its constituents. For this reason our acquaintance with 
inorganic chemical compounds is much more complete than witli 
the organic, for the former may be both decomposed and recom¬ 
posed, while the synthesis of the latter in nearly all cases is yet 
beyond our powers. We will also see that the diseases which 
admit of artificial production are the very ones in whose preven¬ 
tion or treatment we are most successful, and that the discovery 
of the cause and the artificial production of a disease are long 
stops towards its cure. 
Naturally the contagious and infectious diseases, from the 
great mortality which always attends their appearance, have 
attracted the most attention. Some of these are peculiar to sin¬ 
gle species of animals, others are widely transmissible from one 
group to another, and others are common to both man and the 
lower animals, and are communicable from the latter to man ; 
such as glanders, rabies, anthrax, foot and mouth disease and 
tuberculosis, as well as the various parasitic diseases. Until we 
are familiar with the conditions which produce a disease, and this 
knowledge is rarely attainable but through the capability of 
originating that disease, we can never make any decided improve¬ 
ment in treating that disease. All our best-meant efforts will be 
