from an Agricultural and Veterinary Point of View. G9 
regard to the disease had been accumulating, and facts and 
opinions were only too abundant to be made available to any 
extent in this direction. But among the memoirs which the 
calamity had called forth, one of the best was that presented to 
the Academy of Sciences by M. Quatrefages, and a paragraph in 
it had especially attracted the attention of Pasteur. This had 
reference to the discovery by some Italian naturalists of micro- 
scopical bodies — vibratory corpuscles — in the silkworms and 
moths, which Lebert affirmed could always be detected in 
these when diseased, and which Osimo, of Padua, had also 
perceived in silkworms' eggs. Another Italian, Vittadini, had 
even proposed the examination of the eggs by means of the 
microscope, in order to obtain sound ones. The mention of 
this in the ' Memoir ' in question was merely casual, being con- 
sidered of doubtful importance; but it fixed Pasteur's mind on 
the necessity for the employment of the microscope — an in- 
strument which had already rendered him such immense service 
in his experiments on ferments, that its employment again as a 
means of research possessed a strong fascination for him. 
He started on June 6, 1855, for Alais, where the plague raged 
most disastrously, determined not to return until he had mastered 
everything of importance connected with it. In a few hours 
after his arrival he had discovered, and was able to show, the 
corpuscles in certain worms, and after some days' examination 
satisfied himself that these living disease-corpuscles were nu- 
merous in the chrysalides, while there was not one of the moths but 
had them in profusion. In the eggs and the worms the germs 
existed in an imperceptible condition, and the only infallible 
method of procuring healthy eggs, Pasteur insisted, was by having 
recourse to moths free from the corpuscles. This method he had 
proved by experiment to be correct, but critics would not accept 
his statements, and he pursued his enquiry with that scrupulous 
care, intelligence, and pertinacity so characteristic of him, return- 
ing annually to Alais for several months during five years, to 
complete his work. The contagious nature of the disease — 
which was doubted by many, and the manner in which the 
contagion was conveyed — about which there existed several 
opinions among those who believed in its communicability, were 
the first points he determined. To ascertain its contagiousness, 
as well as the mode of infection, he took some healthy worms free 
from corpuscles, and fed them with diseased worms, which were 
pounded and smeared over the mulberry -leaves they ate ; and after 
a certain time the corpuscles, which had already shown them- 
selves in the walls of the intestines, began to appear in the other 
organs, with those red spots on the heads and the rings of the 
bodies, which had caused the disease to be named "pebrine" by 
