Leukemia of the Fowl. QW 
The mononuclear myelocyte with eosinophilic granules is very scarce. 
Scattered through the section are also foci of large mononuclears, or of 
mononuclear myelocytes with eosinophilic granules. Some contain both 
types of cells. They abound in mitotic figures. The liver cells in these 
foci have entirely disappeared. The small, gray nodules consist of cir- 
cumscribed masses of myeloid tissue, usually occupying the periportal 
spaces and composed of a central portion of large mononuclears sur- 
rounded by the mononuclear myelocyte with eosinophilic granules. In 
the blood-vessels and capillaries, the large mononuclear, at times, seems 
to greatly exceed the red blood cell in numbers. 
Spleen.—Except in Nos. 31 and 70, the spleen in every case was en- 
larged (Table 1); usually very much (Fig. 6). The dimensions, in 
contrast to those of the liver, are of definite comparative value. The 
smallest of the enlarged organs measured 3x2x1.7 cm., the largest 
4 x 3 x 2.3 em., the latter being just twice the normal in every 
dimension. 
The weights were strikingly increased. The lowest was 6 gm., the 
highest, 18 gm., 7. e. 18 times the normal, or .6-1.6 per cent of the body 
weight, 7. ¢., 32 times the normal. 
The surface of the spleen may look normal, be reddish brown and 
show beneath its capsule pin-point, gray Malpighian bodies. More fre- 
quently one sees scattered, gray or slightly yellow spots and nodules 
(Fig. 6), the first from 1-3 mm., and the largest of the second from 
0.5-1 cm. in diameter. Again, the organ appears just diffusely gray. A 
section (Fig. 6) appears usually the same as the surface. When dif- 
fusely gray, the pulp is somewhat granular and bulges. Microscopically, 
the entire pulp may be diffusely infiltrated with the large mononuclear 
cell, separating and compressing the Malpighian bodies. In addition, 
circumscribed, closely packed masses of pure large mononuclears or 
mononuclear myelocytes with eosinophilic granules are scattered 
through the section. Again, the myelosis may be present only in 
foci, with practically no disturbance of the normal splenic structure. 
Mitoses are abundant wherever the large mononuclear occurs. The con- 
tents of the blood-vessels are the same as in the liver. 
Heart.—As mentioned above, the external surface of the pericardium 
is frequently covered with a serofibrinous mass. The heart itself may be 
somewhat enlarged, otherwise it appears normal (Fig. 5). Micro- 
scopically also there is little to be seen besides a great excess of the large 
