ASPERGILLOSIS 117 
they are seen to be covered with a fine, short down which later 
disappears quickly and does not return again. The white point en- 
larges and forms a layer 1 or 2 mm. thick adhering to the epidermis 
underneath. The color is generally white or gray. In time the 
thickness of the crusts increases 
as do the surface dimensions. 
Finally the small patches origi- 
nally isolated, coalesce. The ex- 
tension is regular. A white patch 
may reach the dimensions of the 
comb itself. Sometimes the di- 
mensions of a patch remain small 
but it is not rare to observe 
patches 7 or 8 em. long and 3 or 
4 cm. broad on large combs. 
The diseased area examined 
closely presents for study thin 
places and thick places. Those 
which form small hard eminences 
of a grayish white color or slight- 
ly reddened at the top, are irregu- Fic. 11. Favus, involving the head. 
larly disseminated over the area {Drawn from photograph by Sabour- 
aud, Suis and Suffran) 
of the plaque. Between these 
elevations the patch is merely a thin membrane of a pearly white 
color. Wherever the white area is thickened, the scratching detaches 
small fragments like a white powder, of which certain pieces resem- 
ble mica flakes. 
When the lesion in extending, encounters the feathers, its appear- 
ance changes slightly. A deposit of whitish crusts accumulates at 
the base of each feather. Some feathers fall out spontaneously, and 
all those which have this squamous collar at the base, have little re- 
sistance against being plucked. If a feather is pulled it comes out 
entire with its yellow root part, but it bears with it, like a collar, the 
whitish deposit which surrounds the point where the feather emerges 
from the skin. 
Course of disease. The disease is benign. Instances in which 
affected birds become cachectic and die, are exceedingly rare. Re- 
covery may occur in three months spontaneously, or the disease may 
last for years. Long duration may be considered as an example of a 
succession of infections, rather than the persistence of one infec- 
tion. The disease persists in subjects associating with other infected 
