114 DISEASES OF DOMESTICATED BIRDS 
this area that numerous spores may be demonstrated on microscopic 
examination. 
The mycelial threads penetrate the mucosa to the submucosa or 
may enter the adjacent blood vessels forming thrombi and establishing 
an area of necrosis resulting in a nodular formation similar to that 
of tuberculosis. In the abdominal region the organs in contact with 
the air sacs are often involved through adhesions or direct passage 
of the fungus into their interior. 
In the main, the pathologic condition progresses by direct contact. 
Organs affected through the blood stream reveal small areas of ne- 
crosis in which the mycelial threads may be detected. The kidneys 
are more often affected in this manner than the liver. Artificial 
inoculation through hypodermic injection, intraperitoneally or in- 
travenously, produces extensive lesions in these organs. 
The mycelia may be demonstrated microscopically in necrotic 
areas or in nodules in the earlier stages of development. Mycelia 
may also be observed in the mucous membrane lesions, and espe- 
cially in greenish colored areas are spores readily discovered. The 
tissues surrounding the growths are found infiltrated with small 
round cells, leucocytes and connective tissue cells, indicating an at- 
tempt on the part of the system to build a protective wall against the 
spread of the parasite. This attempt is usually abortive although 
evidence of regenerative changes are apparent in some lesions. 
Giant cells are also occasionally present in the tubercle forma- 
tions. 
Course of disease. Among older birds the disease has a tend- 
ency to occur sporadically, more or less extensive intervals elapsing 
between deaths from this cause in a particular flock. Where the ex- 
posure is great, outbreaks of considerable importance may result. 
The resistance of vigorous individuals, however, is high and epi- 
zootics such as are associated with certain other diseases are rarely 
encountered. In grown birds aspergillosis follows a semi-acute or 
chronic course. Death may occur in from 1 to 8 weeks. In brooder 
chicks resistance is less pronounced and acute outbreaks often follow 
exposure to moldy food or material. The disease runs a rapid course 
with fatal termination in 2 to 7 days. Birds confined to limited 
areas as is the case in zoological gardens, show a high percentage 
of fatalities from this cause. 
Diagnosis. Tuberculosis, coccidiosis and aspergillosis are not 
readily differentiated symptomatically in grown fowls. On autopsy 
the lesions are quite distinctive. Tuberculosis principally affects the 
