AVIAN TUBERCULOSIS 93 
birds but are not found in the feces of a very large percentage of 
such birds. 
Tubercle bacilli have been demonstrated in eggs laid by tubercu- 
lous hens but it has not been demonstrated that such a channel of 
dissemination of the infection is an important one. It seems quite 
certain that the disease is not observed in young birds as might be 
expected if transmission through the egg were common. 
Tubercle bacilli, when directly exposed, are sensitive to sunlight, 
but the conditions about poultry establishments are such as to war- 
rant belief that they may persist alive for months. 
Feeding experiments leave no doubt but that the alimentary tract 
is the chief portal for entrance of infective material. Exposure of 
healthy birds by contact with infected birds sets up disease which 
may persist for a year before important lesions develop. The eat- 
ing of carcasses of birds dead of the disease undoubtedly contributes 
to dissemination of infection. In some cases, exposure by feeding 
infected droppings has induced disease that was fatal in six months. 
While the introduction of tuberculous fowls must be regarded as 
the most common means of infecting a flock, there exists the possi- 
bility of its being accomplished by infected pigeons, among which 
the disease is not uncommon, or by pigs. 
Economic importance. Tuberculosis is capable under favor- 
able conditions of causing a very heavy death rate during the course 
of a year. Comparatively few accurate observations have been 
made in this country, but annual losses up to nearly 50 per cent 
have been reported. 
Enough reports are available from the northern half of the United 
States, the Pacific Coast, and Canada to indicate that the disease 
is prevalent in the area mentioned. 
The insidious nature of the disease contributes to the unconcern 
of the owner of an infected flock. Deaths will not occur until the 
flock has been extensively infected and when they occur, are so 
scattered in point of time that they do not cause the same concern 
on the part of the owner as would be occasioned by the same num- 
ber occurring in a short time. Consequently there is lack of in- 
centive to take up repressive measures. 
Prevention. The problem of the control of tuberculosis in 
fowls presents several features that render it much simpler than 
the corresponding problem in cattle. The productive usefulness of 
hens is ended at three years of age, when it is the common practice 
