LEUKEMIA AND PSEUDO LEUKEMIA 147 
Pathogenicity. Leukemia has not been reported as occurring in 
pigeons, turkeys or guinea-fowls and experimental efforts have failed 
to produce the disease in these birds. owls appear insusceptible to 
subeutaneous inoculation but are infected in about 50 per cent of 
cases through intravenous or intraperitoneal injection of a suspension 
of the organs or of the blood of affected fowls. Ellerman and Bang 
observed that inoculation may produce either leukemia or pseudo 
leukemia. 
Course. The duration of the disease is variable. The period of 
incubation ranges from about 2 to 8 weeks. Death may result within 
several days after the appearance of symptoms or may be delayed 
for one to three months. Recovery is only rarely observed. 
Symptoms. While birds may die suddenly from an acute at- 
tack, the manifestations of leukemia are usually of a chronic char- 
acter. There is observed a progressive emaciation with dull, de- 
pressed appearance and noticeable weakness. In some cases the 
abdomen droops. The appetite generally remains good in the 
chronic cases but may fail in acute cases. The comb, wattles and 
skin are pale as a result of the diminution of the red blood cells and 
increase of the white cells. Blood when drawn presents a pale red 
color and fails to clot readily, while. normal fowl blood clots very 
rapidly. 
Morbid anatomy. The carcass has an anemic appearance. Us- 
ually the liver and spleen show the most marked changes. The kid- 
neys are at times also severely involved. The liver may be slightly 
enlarged, congested and sprinkled with minute whitish points, or it 
may be markedly enlarged and congested. Not infrequently rupture 
of the liver resulting in internal hemorrhage is observed. The en- 
larged liver may appear much darkened, soft and pulpy in more 
acute cases. In cases of longer duration, this organ is greatly en- 
larged and pale in appearance or else mottled and sprinkled with 
grayish white spots. It has a firm consistency and rigid contour. 
On cut section the tissue appears bloodless. The spleen generally 
shows changes in conformity with those cf the liver. It may be 
only slightly congested or may be greatly enlarged and congested. 
As in the case of the liver, the consistency varies from soft and 
pulpy to a firm, compact mass. The color is bright mahogany in 
the case of severe congestion and sometimes grayish and brownish 
in spots. The kidneys may be several times the normal size, con- 
gested in the early stage or firm and pale at a later period. The 
intestine appears pale on the serous surface but areas of congestion 
