94 DISEASES OF DOMESTICATED BIRDS 
to market the birds for table use, if this indeed is not done after 
two years. Thus total replacement of stock is possible in a short 
period. The extensive use of incubators and brooders assures the 
isolation of the young from infected old birds. Where the business 
is conducted on an intensive scale on a small area, isolation of birds 
of various ages is quite often practiced. Thus ideal conditions for 
combating the disease already exist in certain plants, if indeed the 
disease does ever make considerable progress under such conditions. 
It is undoubtedly true that the disease only becomes serious when 
there is unlimited opportunity for mingling of birds of various ages 
as exists where poultry are kept without restraint. This is the con- 
dition in the average small poultry yard, or in an extensive poultry 
business where the system of using unfenced colonies is practiced. 
In attempting to control the disease among unfenced birds, the 
end sought is to secure isolation of young birds and maintain it 
throughout life. 
In every extensively infected flock there will be a certain number 
of badly diseased, worthless birds, which may be recognized by 
physical means, and destroyed. The intradermal test may be ap- 
plied to determine the extent of the infection. The results of this 
test, the age of the birds and egg yield, will aid in reaching a de- 
cision as to whether all or part should be marketed at once. Many 
reacting birds will be found at autopsy, to contain very minute 
lesions and there should be no prejudice against killing such for 
food. 
Appropriate disinfection of contaminated buildings, and tempo- 
rary abandonment of areas of soil too large to disinfect, will natur- 
ally suggest themselves. 
Van Es reports upon results of testing a flock of 249 birds, of 
which 43.37 per cent were tuberculous. All reacting and undesir- 
able birds were eliminated, leaving 56 non-reacting birds. These, 
together with 47 birds purchased after the test, increased the next 
year to 249. One bird died of tuberculosis after the first test and 
had undoubtedly failed to react on account of severe lesions. A 
second test made a year after the first one revealed 2.41 per cent of 
reactors. These were regarded as having contracted the disease 
from the one non-reactor of the first test. 
Mention of hygienic measures such as good ventilation, sunlight, 
and warm quarters has no place in a discussion of the control of 
tuberculosis in fowls. The disease is a veritable scourge in parts 
of California where such hygienic conditions are most favorable. 
