MICROBES IN THE HUMAN BODY 47 



barrier has been pierced by a little wound permitting the 

 passage of the bacteria. This happened in the case of Pasteur's 

 sheep, which took anthrax when he fed them with anthrax 

 spores mixed with minute splinters. But this explanation does 

 not hold for all cases. Numerous facts exist which establish 

 the permeability of the healthy mucous membrane. 



The importance of the problem was perceived when the 

 conditions of infection with tubercle began to be discussed. 

 Behring thought, in agreement with Chauveau, that the bacillus 

 penetrates into the body of man and cattle, not only by the 

 respiratory passages, but also through the digestive tract. This 

 idea was suggested to him by the predominance of mesenteric 

 lesions in infantile tuberculosis, compared with the predomin- 

 ance of pulmonary lesions in the adult ; he thought that 

 tuberculosis always began in childhood in the intestine and 

 did not invade the lung until maturity. The intestine of an 

 adult, he maintained, does not permit the passage of the 

 bacteria as does that of a child, the reason being that in the 

 infant,\ as in general among new born animals, the intestinal 

 mucosa is not coated with the continuous and perfect covering 

 which develops later ; the covering is discontinuous, inter- 

 rupted and open to the passage of bacteria. No intestinal 

 lesion can be found because none exists : there has been 

 penetration without violence. 



Bering's idea has been developed to such an extent that 

 some observers declare that invasion by the intestine is more 

 frequent than invasion by the lung ; and during the search for 

 proofs and comparisons they have studied closely the penetra- 

 tion of the intestine not only by the bacillus of tuberculosis, 

 but by various other bacteria, pathogenic and non-pathogenic, 

 and even by inert dust particles. Pulmonary anthracosis, the 

 disease or rather the histological condition which consists in the 

 impregnation of the lungs by carbon particles from the air of 

 mines and factories, has formed the field of battle for the 

 partisans and opponents of Behring's idea, and a multitude of 

 experiments have resulted, not without instructive consequences. 



Dust particles can reach the lung by passing through the 



