SPIROCHETOSIS AND RARE INFECTIOUS DISEASES 137 
lation is made with virulent blood through the skin, the period of 
incubation ‘is reduced to a period varying from 48 to 72 hours. The 
period of incubation is longer when the virus is placed on the skin 
superficially. 
The disease is acquired easily through the mouth, especially if the 
virulence of the parasite has been raised by a number of passages. 
Symptoms. Very commonly the disease occurs in such an acute 
form that birds apparently healthy at night are found dead under 
the roost in the morning. In the less rapidly fatal form there is 
dullness, ruffling of the feathers, somnolence and diarrhea. The 
comb becomes pale as a result of anemia. The temperature reaches 
110° or 112° F. but drops abruptly at the crisis, which coincides 
with the disappearance of the spirochetes from the circulating blood. 
During the course of the disease, there is a marked decrease in the 
number of red corpuscles and a leucocytosis characterized by increase 
in the number of polynuclear leucocytes. After the crisis, the poly- 
nuclear cells diminish and the mononuclear cells increase in num- 
ber. The acute type of disease may be terminated by death in from 
four to five days after the onset of symptoms. Death often occurs 
during convulsions. 
The chronic type may follow the acute phase or appear inde- 
pendently. Death may not occur for fifteen days. Paralytic symp- 
toms are noted. The wings may droop, or the head be twisted back, 
or the legs may be involved. Inability to use the claws is an early 
symptom of leg paralysis. There may be disturbances of gait, and 
the bird may appear knock kneed or bowlegged. Emaciation and 
anemia are also particularly characteristic of the chronic type. 
Morbid anatomy. In birds dead of an acute attack, the spleen 
is found to be enlarged to several times normal. The liver also is 
greatly enlarged, shows fatty degeneration and sometimes focal ne- 
crosis. The other organs do not usually show marked lesions beyond 
the paleness of muscles, lungs and kidneys resulting from the ane- 
mia. The intestines sometimes are congested, and show punctiform 
hemorrhages. In chronic cases on the other hand, the liver and 
spleen are smaller than normal. 
The skin shows evidence of tick bites in the form of subcutaneous 
hemorrhagic areas. 
Microscopic examination of the blood of a bird dead of the disease, 
or during life after the crisis, will not reveal spirochetes. 
Life cycle of spirochetes. After the spirochete in the blood 
reaches a length of 16 to 19 microns it divides by a transverse divi- 
