36 DISEASES OF DOMESTICATED BIRDS 
“ Léfler’s Blood Serum. After twenty-four hours’ growth at 37.5° C, 
the path of the needle is marked by a white, raised growth, with shiny, con- 
toured or smooth surface and undulate border. The condensation liquid 
becomes decidedly turbid. After several days the surface of the growth 
becomes dull. The liquid is then observed to contain a viscous sediment 
and to have patches of pellicle floating upon the surface. 
“Indol. A positive reaction is obtained in sugar-free bouillon cultures. 
“Animal Inoculation. Subcutaneous or intravenous injection of fowls 
with 1 c.c. of a 24-hour bouillon culture resulted in death in about fifteen 
hours. Doses as small as 0.05 cc. killed in about three days. A young 
rabbit inoculated with 0.5 ec. in an ear vein was found dead fourteen 
hours later. A guinea pig inoculated with 1 cc. subcutem was found 
dead in fourteen hours. Another receiving 0.5 ec. subcutem survived 
thirty-six hours. A pigeon swallowing 1 c.c. died in twenty-one hours, and 
another receiving 0.12 c.c. subcutem was found dead fourteen hours later.” 
Pathogenicity. Besides common fowls, geese, ducks, turkeys, 
pheasants, pigeons and a large number of wild birds are susceptible 
to infection. Hemorrhagic septicemia in geese is discussed in Chap- 
ter XIX. 
The virulence of the fowl cholera organism varies greatly. Had- 
ley has shown that the minimum lethal dose for fowls may lie at 
any point between 10 c.c. and 0.000,000,000,000,001 e.c. of a 48 
hour bouillon culture. Hadley states that infection results from 
the inoculation into the breast muscle of less than fifty organisms 
and probably by the inoculation of no more than four. To test the 
infectiveness of the carcasses of fowls dead of the disease in a natural 
outbreak, Ward fed such material to ten healthy cockerels. On the 
first day following the exposure by feeding, three birds were dead; 
on the second day, three; on the third, fourth, fifth and sixth days, 
one bird each died. The incubation period may vary from eighteen 
hours to as many days. 
The blood and all discharges of a sick bird are infective. Eggs 
have been demonstrated to contain the virus. 
Infection may be induced in very small doses in a large variety 
of ways such as ingestion, subcutaneous, intravenous or intramus- 
cular injection, introduction of culture into the conjunctival sac, or 
into the scarified skin. 
Repeated passage of the virus through birds or through guinea 
pigs results in an increase of virulence of a strain. On the other 
hand diminution of virulence occurs under conditions not well un- 
derstood. Doubtless there are also variations of virulence with re- 
spect to the species attacked during various outbreaks. 
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