It was noticed, however, that with each transference of the virus to a new organic body the bacilli were modified somewhat in form and activity.  They became, so to speak, less savage.  The bacterium which at the beginning had been for its savagery a wolf, became in the second body a cur; then a hound; then a spaniel; and then a diminutive lapdog!  The bacteria were thus said to be “domesticated;” for the process was similar to the domestication of wild animals into tame.  The virus was said to be “attenuated;” that is, made thin or fine; that is, its poisonous and death-dealing quality, was so reduced as to make it comparatively innocuous.

If after the process of attenuation was complete—­if after the bacteria were once thoroughly domesticated and the poison produced by them be then introduced into a well subject, that subject would indeed become diseased, but so mildly diseased as scarcely to be diseased at all.  In such a case the result was of a kind to be called in popular language a mere “touch” of the disease.  In such case the severe ravages of the malady would be prevented; but the subject would be rendered incapable of taking the disease a second time.

On this line of fact and theory Pasteur successfully pressed his work.  One disease after another was investigated.  It was demonstrated in the case of both the lower animals and men that a large number of maladies and plagues might be completely disarmed of their terrors by the process of inoculation.  The name of Pasteur became more and more famous.  The celebrated Pasteur Institute was founded at Paris, under the patronage of the French Government, and in some sense under the patronage of the whole world.  To this establishment diseased subjects were taken for treatment, and here experimentation was carried on over a wide range of facts.

The value of the results attained can hardly be overestimated.  The fear which mankind have long entertained on account of plagues and epidemics, and the loss which the animal industries of the world have sustained, were largely abated.  As yet the use of the Pasteur methods for the prevention and cure of disease is by no means universal; but the knowledge which has come of his investigations and of the results of them has diffused itself among all civilized nations, and the hygienic condition of almost every community has been most favorably affected by the new knowledge which we possess of bacteria and of the means of destroying them.

Pasteur, whose recent death has been mourned by the best part of mankind, was an explorer and forerunner.  His industry in his chosen field of investigation was prodigious.  When he was already nearly seventy years of age, he undertook the investigation of hydrophobia, with the purpose of discovering, if he might, the germ of that dreaded disease, thus preparing a method for inoculation against it.