562 
A. O. ZWICK. 
unfortunately, is still accepted by many, rests on the assumption 
that the most important source of tubercular infection is finely 
pulverized tuberculous material, suspended in the air, as dust, and 
the direct exposure of the lung to this dust through the process 
of respiration. And, of course, if this so-called “ inhalation the¬ 
ory ” represents the truth, and, further, if it were a fact, as many 
of those who maintain it, assert, that tubercle bacilli cannot pass 
through the uninjured wall of the digestive tract and reach or¬ 
gans remote from it without leaving evidences of their passage, 
then tubercle bacilli in dairy products have no important sig¬ 
nificance for the public health. 
That is why there has been given so much thought to the 
mode of infection, to the gateway through which the bacilli en¬ 
ter the body. 
But as long ago as 1868 to 1874, Chavreau brought about 
pulmonary tuberculosis by the ingestion (per vias natnrales) of 
tubercular material zvithont producing pathological conditions in 
the digestive tract. 
And recent investigation prove more and more conclusively 
that the introduction of the tubercle bacilli into the body with 
food may lead directly to the development of pulmonary tuber¬ 
culosis without lesions in the alimentary canal and without inter¬ 
mediate lesions of disease on the pathway between the digestive 
and respiratory organs. 
The most important investigations on this subject are prob¬ 
ably those of Calmette and his associates, among whom my 
teacher, Georges Petit, of Paris, 1907. 
These investigators claim, and are worth quoting in full in 
support of their claim, that dust particles never penetrate further 
into the lung than to the first branches of the bronchi; that tuber¬ 
culosis is constantly a disease, the infection of which enters 
through the intestines; that tubercle bacilli may penetrate the in¬ 
testinal wall zvithont causing lesions (how, I have shown you) ; 
that the bacilli may pass through the mesenteric glands without 
causing lesions; that the bacilli frequently cause primary lesions 
in the mesenteric glands of young experiment animals (because 
