THE MICROBES OF HUMAN DISEASES. 173 
as long as the epidermis of the mucous membrane 
covering the intestinal canal is healthy. Pasteur has 
shown that they are not found in the blood of a 
healthy man, but that the slightest lesion of the 
mucous membrane suflices to introduce them into the 
circulation.* This fact was proved by experiments 
made at Pouilly-le-Fort on sheep, inoculated with the 
anthrax microbe by means of their food. The mortality 
among these animals was notably increased when 
a 18.—Spirochete buccalis, and S, plicatilis, b (mixed with Vibrio rugula, 
Figs. 77, eee a), microbes in mouth of a healthy man. : 
thistles, bearded grain, or sharp-edged leaves were 
mixed with their food, so as to cause little wounds in 
their mouths, each of which served as an entrance for 
microbes. As long as the microbes are few in number, 
they perish quickly in the blood; but when the 
number is considerable, the organism has not the power 
to destroy them ; they soon compete with the corpuscles 
of the blood, and the most serious diseases ensue. 
Miquel estimates the number of spores introduced 
into the human system by respiration, when the health 
* This is not the case with fishes. Richet and Ollivier have shown 
that microbes are normally found in the blood of sea-fish, without 
affecting their health. 
