took a culture of bovine bacilli, which were entirely harmless to fowls,
and, inclosing them in a collodion capsule, inserted them into the
peritoneal cavity of a hen. The collodion capsule permitted the fluids
of the body to enter and provide food for the bacilli, but prevented the
admission of the leucocytes to attack and destroy them. After several
weeks the capsule was removed, the bacilli found still alive, and
transferred to another capsule in another fowl. When this process had
been repeated some five or six times, the last generation of bacilli was
injected into another fowl, which promptly developed tuberculosis,
showing that by gradually exposing the bacilli for successive
generations to the high temperature of the bird's body (from five to
fifteen degrees above that of the mammal), they had become acclimated,
as it were, and capable of developing. So that it is certainly quite
conceivable that bovine bacilli introduced in milk or meat might manage
to find a haven of refuge or lodgment in some out-of-the-way gland or
tissue of the human body, and there avoid destruction for a sufficiently
long time to become acclimated and later infect the entire system.

This is the method which several leaders in bacteriology, including
Behring (of antitoxin fame), believe to be the principal source and
method of infection of the human species. The large majority, however,
of bacteriologists and clinicians are of the opinion that ninety per
cent of all cases of human tuberculosis are contracted from some human
source. So that, while we should on no account slacken our fight against
tuberculosis in either cattle or birds, and should encourage in every
way veterinarians and breeders to aim for its total destruction,--a
consummation which would be well worth all it would cost them, purely
upon economic grounds, just as the extermination of human tuberculosis
would be to the human race,--yet we need not bear the burden of feeling
that the odds against us in the fight for the salvation of our own
species are so enormous as they would be, had we no natural protection
against infection from animals and birds.

The more carefully we study all causes of tuberculosis in children, the
larger and larger percentage of them do we find to be clearly traceable
to infection from some member of the family or household. In Berlin, for
instance, Kayserling reports that seventy per cent of all cases
discovered can be traced to direct infection