Diseases of the Respiratory System 175 



Lesions of the second type are whitish or yellowish tuber- 

 cles resembling the tubercles of tuberculosis. They vary in 

 size from the head of a pin to a large pea. The tubercles are 

 embedded in the tissues of the walls of the air passages, in 

 the lungs and sometimes also in the liver, spleen and kid- 

 neys. Each tubercle contains a growth of mold at the cen- 

 ter which is inclosed by a wall of animal cells. 



A certain diagnosis of aspergillosis requires the identifica- 

 tion of fungus filaments and spores within the lesions. 

 This is of course impossible during the life of the bird. 



Etiology. — The disease is caused by molds of the genus 

 As-pergillus which grow on the mucous membrane of the air 

 passage. The four parasitic species in order of their impor- 

 tance are Aspergillus fumigatus, Aspergillus nigrescens, Asper- 

 gillus glaucus, Aspergillus candidus. The appearance of one 

 of these molds, when greatly magnified, is shown in Fig. 32. 



These molds and their spores occur on dead organic ma- 

 terial like straw, grain, etc. They are inhaled in breathing or 

 swallowed with the food. This being the case the importance 

 of avoiding musty litter, and moldy or musty grain of all 

 kinds is apparent. As with most other diseases the resistance 

 of the individual against infection is here an important mat- 

 ter. Some fowls will be able to stand musty litter and grain 

 without any harm, while others will promptly develop asper- 

 gillosis. When once present in a flock aspergillosis is prob- 

 ably transmitted from generation to generation through the 

 eggs. 



Treatment. — The disease is prevented by having clean, 

 dry, well ventilated houses and avoiding the use of moldy 

 litter or grain. Vigorous birds under sanitary conditions are 

 fairly resistant. 



Since the disease probably sometimes spreads from bird to 

 bird, affected individuals should be killed or isolated and the 

 bodies of dead birds burned. Salmon says that " sometimes 



