136 DISEASES OF DOMESTICATED BIRDS 
1.5 per cent solution of sodium citrate in a .9 per cent solution of 
sodium chlorid. A piece of kidney of a normal rabbit or a piece of 
pectoral muscle of a fowl is placed in a test tube. Ascitic fluid is 
added to make the column of fluid 10 em. high or about 10 to 15 ¢.c. 
To this is added a few drops of the infected blood. The fluid is 
covered with a layer of paraffin oil that has been autoclaved twice. 
Ascitie fluid is not always suitable and it may be necessary to try 
many lots. 
The maximum growth is reached at about the fifth day, the cells 
being fully developed typical spirochetes. After the fifth day de- 
generation of the cells begins and proceeds slowly. The organism has 
been demonstrated to remain virulent for chickens through 13 gen- 
erations of culture. However, under certain cultural conditions it 
may lose its virulence. The inoculation of birds with such aviru- 
lent strains induces a resistance to subsequent infection with a viru- 
lent strain. 
Pathogenicity. Fowls, geese, ducks, guinea-fowls, turtle doves 
and sparrows have been reported as susceptible. Animals com- 
monly employed in laboratory work are immune, but Levaditi re- 
ports that he produced a transitory spirochetosis in a rabbit lasting 
three or four days. 
Poultrymen, when spirochetosis occurs, are apt to attribute losses 
to excessive tick infestation and to the resulting loss of blood with- 
out recognizing that an infectious disease is the cause of the losses. 
The prevalence of the disease will coincide with the season that 
is most favorable to the multiplication of ticks, but deaths will oc- 
cur at any time when susceptible stock is introdneed, providing ticks 
are at all active. 
Bevan notes that birds in infected flocks become immune. How- 
ever, the birds previously immune will succumb after the introduc- 
tion of newly arrived susceptible birds starts the infection anew. It 
is possible that the passage through susceptible birds increases the 
virulence of the virus. 
Upon introduction of infection into a flock hitherto uninfected, 
spirochetosis may be exceedingly fatal and exterminate a flock in a 
few days. Young birds are particularly susceptible. 
The course of the experimentally produced disease varies accord- 
ing to the method of the introduction of the virus, the activity of 
the spirochetes and the receptivity of the bird. Wher the inocu- 
lation is made by means of the tick, after 6 to 8 days and sometimes 
more, the spirochetes are encountered in the circulation. If inocu- 
