92 DISEASES OF DOMESTICATED BIRDS 
dose varies from one-twentieth to one-thirtieth of a cubic centimeter. 
After short experience, attention to the graduations on the syringe 
will be abandoned and the dose judged by the appearance of the tis- 
sues at the point of injection. The head of the fowl should be held 
with considerable firmness by an assistant during the injection, in 
order to obviate the necessity for inflicting unnecessary damage to 
the tissues, which would interfere with observing the results. Care 
must be taken to avoid injury of the wattle by rough handling. 
A positive reaction to the test consists of a swelling of the in- 
jected wattle. Perhaps ten per cent of the swellings will be so 
slight as to be doubtful. Observations made by Van Es and Schalk 
indicate that among the reactions considered by them as doubtful, 
about one-half were found on slaughter, to contain lesions, and half 
to be free from lesions. The majority of reactions will leave no 
doubt as to the existence of a pronounced edematous swelling, which 
may increase the thickness of the wattle to several times normal. 
Of 90 birds tested by Van Es and Schalk, showing typical reac- 
tions, 88 were found tuberculous at slaughter and 2 showed no vis- 
ible lesions. Of 130 birds slaughtered and found without lesions, 
120 or 91.5 per cent had failed to react to the test. About 8.5 per 
cent of the non-reacting fowls were found to have lesions. Thus the 
results shown indicate that the intradermal tuberculin test for fowls 
is about as accurate as the same test or the subcutaneous test in 
catile. 
The test surely furnishes information regarding the extent to 
which infection has spread in a flock and consequently provides in- 
formation regarding which birds should be eliminated. Of three 
and four year old birds in an infected flock, as high as 86 per cent 
may react. Of two year olds, 24 per cent and of pullets, 3 per 
cent have reacted. It may further be of use in determining whether 
or not tuberculosis exists in a flock from which it is contemplated 
to purchase. birds. 
Transmission. The tendency of lesions involving the intestine 
to perforate the wall and discharge into the lumen, provides the 
main channel for the dissemination of tubercle bacilli. Microscopie 
examination of such lesions reveals enormous numbers of the or- 
ganisms. In view of the rarity of pulmonary lesions and the rela- 
tive frequency with which intestinal lesions occur, the feces must be 
regarded as the chief channel of elimination of infection. Tubercle 
bacilli have been demonstrated to be present in the feces of infected 
