lus tuberculosis_, although there are varieties of this
organism found in different species of animals that are sufficiently
distinct to permit of recognition.

The question of prime importance is, whether the bovine type is
transmissible to the human or not. Artificial inoculation of cattle with
tuberculous human sputum as well as pure cultures of this variety show
that the human type is able to make but slight headway in cattle. This
would indicate that the danger of cattle acquiring the infection from
man would in all probability be very slight, but these experiments offer
no answer as to the possibility of transmission from the bovine to the
human. Manifestly it is impossible to solve this problem by direct
experiment upon man except by artificial inoculation, but comparative
experiments upon animals throw some light on the question.

Theo. Smith[81] and others[82] have made parallel experiments with
animals such as guinea pigs, rabbits and pigeons, inoculated with both
bovine and human cultures of this organism. The results obtained in the
case of all animals tested show that the virulence of the two types was
much different, but that the bovine cultures were much more severe.
While of course this does not prove that transmission from bovine to
human is possible, still the importance of the fact must not be
overlooked.

In a number of cases record of accidental infection from cattle to man
has been noted.[83] These have occurred with persons engaged in making
post-mortem examinations on tuberculous animals, and the tubercular
nature of the wound was proven in some cases by excision and
inoculation.

In addition to data of this sort that is practically experimental in
character, there are also strong clinical reasons for considering that
infection of human beings may occur through the medium of milk.
Naturally such infection should produce intestinal tuberculosis, and it
is noteworthy that this phase of the disease is quite common in
children especially between the ages of two and five.[84] It is
difficult to determine, though, whether primary infection occurred
through the intestine, for, usually, other organs also become involved.
In a considerable number of cases in which tubercular infection by the
most common channel, inhalation, seems to be excluded, the evidence is
strong that the disease was contracted through the medium of the milk,
but it is always very difficult to exclude the possibility of pulmonary