555 
or cells, which have fine hairlike processes that are in constant motion, 
and the motion is of a kind that tends to move dust, etc., outward 
and not farther into the lung. 
From this it should readily be seen that the inhalation theory to 
account for the infection of the lung is simple only when we fail to 
analyze it, and that analysis shows it to be a practically impossible 
hypothesis. 
The normal channel through which material from without enters 
the bod}^ is the digestive canal. It has been shown by Nicolas and 
Descos, Ravenel, Schloszmann and Engle, Calmette and his asso- 
ciates, and other bacteriologists and pathologists too numerous to 
mention, that tubercle bacilli may .penetrate rapidly through the 
healthy walls of the intestines and reach the great thoracic lymph 
duct. The thoracic lymph duct empties its contents into one of the 
large veins that communicate with the heart; mixed with the blood 
in this vein the material from the duct enters the heart and is pumped 
directly to the lung, where it is filtered through the lung capillaries, 
which are the finest and most complex capillaries of the body. If we 
recall that the careful anatomical examinations made by Aufrecht 
and by Calmette and his associates proved that the tuberculous proc- 
esses in the lungs have their beginning in the finer capillaries and 
not in the finer air tubes, we are in a position to conclude that infected 
food much more than infected air is to be dreaded as a cause of 
tuberculosis. 
Tuberculosis among dairy cows is so common and wide spread that 
we can not hope to clean all dairy herds of the disease for some time 
to come; hence it is necessary for the protection of health to avail 
ourselves of the one expedient which is immediately at hand, and 
that is pasteurization ; and pasteurization should not be restricted to 
milk, but all milk, cream, etc., used in the manufacture of butter, 
cheese, and other dairy products, should be pasteurized, unless it is 
obtained from healthy, nontuberculous cows that are stabled under 
hygienic conditions in an environment wholly free from tuberculous 
infection. 
The elimination of tuberculosis from the dairy herd is urgently 
recommended, not only because the protection of public health re- 
quires it, but also because tuberculosis among cattle is a serious cause 
of pecuniary loss, so serious indeed, that, from the strictly economic 
point of view, it must be regarded as the most important problem 
those who are interested in animal husbandry can undertake to solve. 
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