AVIAN TUBERCULOSIS 91 
A form of nodular disease of the skin has been observed in which 
tubercle-like organisms are found, and efforts to cultivate them give 
negative results. Another point of difference is that the organisms 
are decolorized by acidulated alcohol, which does not occur in the 
case of true avian tubercle bacilli. Unquestionable tuberculous le- 
sions of the skin occur in pigeons. A tuberculous lesion consisting 
of a cutaneous horn is relatively common in parrots. 
. Bone lesions have been observed particularly on the breast bone 
and ribs. Lesions occur in the knee, back, digital and shoulder 
joints. The extremities of the bones enlarge with accumulation of 
cheesy material, or may discharge a semi-fluid substance. 
Differential diagnosis. A diagnosis of tuberculosis by physical 
examination of the living bird is hardly possible in most cases, nor 
is this important. Emaciation creates a strong presumption of the 
existence of tuberculosis but is not conclusive, for it occurs in as- 
thenia, in serious infestation with air sac mites and in other condi- 
tions less well understood. 
At autopsy of fowls, the possibility of the occurrence of tumors 
of the liver, and nodular teeniasis of the intestines should be borne 
in mind. Nodular lesions not involving the liver and spleen, may 
quite safely be considered as not tuberculosis. In the turkey the 
more highly colored areas occurring in infectious entero hepatitis 
are not likely to mislead one familiar with these lesions. Gouty 
arthritis and bumblefoot in the fowl are. suggestive of tuberculosis. 
Nodules in the lung caused by aspergillosis may be differentiated 
from tuberculosis by microscopic examination. 
Microscopic examination of smears for tubercle bacilli is available 
as a means of diagnosis, especially since organisms are unusually 
abundant in lesions of avian tuberculosis. 
Tuberculin test. Numerous efforts have been made to apply 
the subcutaneous tuberculin test to fowls, using tuberculin prepared 
from both avian and mammalian cultures, but without success. 
Better results have attended trials with the intradermal (intra- 
cutaneous) form of the test in manner similar to that in which it 
is applied to cattle. The wattle is chosen as the site of injection 
and a very fine needle of No. 26 or 27 gauge is employed. The aim 
is to deposit the tuberculin not in the deeper layers, but in the 
stratum Malpighii. It should not be injected so superficially that 
the tuberculin will be lost by rupture of the epithelium. 
The tuberculin employed is prepared in the usual manner from 
an avian tubercle culture, and is diluted fifty per cent for use. The 
