543 
The nearly unanimous opinion of the members of the recent Inter- 
national Congress on Tuberculosis at Washington, D. C., was that 
the tuberculous dairy cow is a serious menace to public health. 
It does not seem necessary to add, as could easily be done, to this 
evidence to prove that the various existing types of tubercle bacilli 
are simply mutation forms of one specific organism. The presence of 
transition forms between human and bovine types; the occurrence of 
pure bovine t}^pes in human lesions and of human types in bovine 
lesions; the occurrence of bacilli highly virulent for cattle in human 
lesions ; the generally greater virulence of bovine types for all species 
of animals ; and the virulence, and greater virulence, of bovine types 
for anthropoid apes and monkeys,® or the animals in the zoological 
scale most nearly related to man, are all facts that support the conclu- 
sion that tubercle bacilli in dairy products are a source of great 
danger to public health. 
It is true that tuberculosis is more commonly an affection of the 
lung than of other portions of the body. The explanation for this, 
which was long regarded as satisfactory and is still accepted by many, 
rests on the assumption that the most important source of tubercu- 
lous 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. If this so-called “inhalation” 
theory is true, and as many of those who maintain it assert, tubercle 
bacilli can not pass through the uninjured wall of the digestive tract 
and reach organs remote to it without leaving evidences of their 
passage, then tubercle bacilli in dairy products have no important 
significance for public health. Therefore to 'prove that tubercle 
bacilli in dairy products are dangerous we must give some thought to 
the mode of infection, or the portal through which the bacilli enter 
the body. 
How strongly the inhalation theory was intrenched in the minds of 
medical men is well expressed by Aufrecht^ in the statement that 
considerable courage was required only a few years ago to character- 
ize it as an unwarranted hypothesis for the wide belief of which no 
satisfactory evidence had been supplied. He, in 1900, and Baungar- 
ten,® in 1901, pointed out that it had not been proven to be the exclu- 
sive or even the most important mode of infection with tuberculosis. 
In 1902 followed the experiments of Nicolas and Descos,** confirmed 
by those of Eavenel ® in 1903, which proved that tubercle bacilli 
® Report of the British royal commission in the British Journal, No. 2430, 
1907 ; also, Bureau of Animal Industry Bulletin No. 52, 1905. 
^ Berliner Klinisch Wochens., No. 27, 1907. 
® Wiener Med. Wochens., Vol. 51, No. 44. 
^ Jour. Phys. et de Path. Gen., VoL IV, 1902. 
® Jour, Med, Resea., Vol. X, pp. 460-462. 
