82 DISEASES OF DOMESTICATED BIRDS 
The virus is believed to be transmitted naturally by nasal and 
oral secretions, by the droppings of diseased birds or by eating 
carcasses of dead birds. Wounds of the skin when contaminated 
with virus readily result in infection. Mites (Dermanyssus avium) 
have been tested as to their ability to transmit the disease, with nega- 
tive results. Likewise ticks have given negative results. 
The disease is most frequent in early spring, declines in preva- 
lence in the summer and does not occur during the winter. In arti- 
ficial transmission, fowls succumb to subcutaneous or intramuscular 
injection or to application of the virus to the scarified skin. They 
likewise become infected by ingestion. a 
After the subcutaneous or intramuscular injection of moderate 
amounts of heart blood and pieces of spleen or kidney the size of 
a pea the inoculated hens die as a rule within 36 to 48 hours, often 
in 3 to 4 days, and quite rarely only after 5 to 7 days. Feeding of 
larger amounts of pieces of organs causes death after about the same 
length of time or a few hours longer than in the case of subcutane- 
ous injection. Filtrates of nasal mucus, contents of the small in- 
testine, bile, brain, blood and internal organs are infective for hens. 
Many authors have failed to transmit the disease to old and young 
ducks or to young pigeons. Young geese are susceptible to sub- 
cutaneous and intramuscular inoculation or by the mouth, and die 
as a rule after about seven days. On the other hand, old geese 
are very slightly susceptible to ordinary methods of inoculation, 
Subdural inoculation of these has succeeded, and caused the nervous 
type of the disease. 
The disease exhibits peculiarities in showing a preference at dif- 
ferent times for different species of birds all in contact with one 
another, such as fowls, pigeons, geese and ducks. Mammals are 
immune to infection. 
In young geese and in pigeons the disease assumes the nervous 
type, which runs a much less rapid course. In these the virus at 
first localized in the blood corpuscles seems to disappear therefrom, 
and becomes established in the central nervous system. However, 
the virus may reappear in the blood shortly before death. 
Cominotti has observed the nervous type of the disease in wild 
ducks in confinement under conditions resembling those under which 
domesticated birds are kept. The virus was found always in the 
central nervous system and was never demonstrated in the blood or 
the internal organs even when large quantities of inoculating mate- 
rial were used. Transmission of the infection from wild ducks to 
