234 Diseases of Poultry 



feathers becomes surrounded by concentric rings of the scaly 

 material. The feathers become dry, erect, and brittle and 

 finally break off or fall out leaving a disk-shaped scale with a 

 depression at the bottom where the base of the feather was 

 located. The bird's head and neck and patches around 

 the vent become bare of feathers. The exposed skin 

 is covered with the cup-shaped scales. Sometimes the 

 disease spreads over the whole body until the bird becomes 

 nearly naked. The diseased bird has a peculiar disagree- 

 able odor, sometimes likened to the odor of a musty 

 grain or to moldy cheese and sometimes to cat's urine or to 

 macerating animal material. In early stages the general 

 health does not appear to be affected, but as the disease 

 advances the bird loses its appetite, becomes poor and 

 exhausted, and finally dies. 



Etiology. — The disease is caused by the fungus Achorion 

 schonleinii. 



This fungus is found in the cup-like scales on the skin and in 

 the quills of the feathers of the diseased parts. If the favic 

 cups or scales are moistened with weak acetic acid and exam- 

 ined under the microscope, it will be seen that they are 

 formed of branching, thread-like mycelial tubes of the fungus 

 closely interwoven with one another, spores of the fungus, 

 and epithelial scales from the skin of the host embedded in a 

 viscid substance secreted by the fungus. Some of the tubes 

 of the mycelium contain spores. Many of the spores are 

 found free among the filaments. They are usually found in 

 groups of 3, 4, or 8. 



Both the mycelium and spores of the fungus are found in 

 the quills of the feathers of the diseased parts. The fungus 

 sometimes penetrates even the barbs of the feathers. 



Favus is a contagious disease and gets into a flock by the 

 introduction of an affected bird. It is less likely to attack 

 strong, vigorous birds than those in poor condition. It 



