CHAPTER XIV 
LEUKEMIA AND PSEUDO LEUKEMIA 
Characterization. Leukemia in fowls is a disease of the blood, 
and blood forming organs. It is marked by changes in the com- 
position of the blood manifested principally by an enormous in- 
crease in the number of leucocytes and an accompanying decrease in 
the number of erythrocytes. Besides these changes, lymphoid en- 
largement of the liver, spleen and kidneys is usually to be observed. 
Pseudo leukemia is a term designating a condition in which lymph- 
oid tissue is present in the various organs, without changes in the 
circulating blood. The two conditions are very closely related, if in- 
deed they are not different stages of the same process. 
History. The disease in fowls was first recognized by Warthin 
in 1907 and soon after by Ellerman and Bang. Butterfield in 1905 
and Yutaka Kon in 1907 very likely observed cases of leukemia, 
but did not examine the blood. Pickens presents a thorough survey 
of the literature of the disease accompanied by original observations 
on a series of cases. The disease has been reported in Denmark, 
Germany and the United States. 
Etiology. Ellerman and Bang and also Yutaka Kon found pro- 
tozoa-like bodies in the organs and bone marrow of affected fowls. 
The significance of these bodies has not been definitely determined. 
In typical cases of leukemia encountered by the present writers, at- 
tempts to isolate an organism from the blood and parenchymatous 
organs have given negative results. The fact that Ellerman and 
Bang succeeded in transmitting leukemia to fowls by intravenous 
and intraperitoneal injection of a cell free filtrate of infected exu- 
dates, points to an ultra-microscopic virus as the causative agent. 
The disease is readily transmitted by non-filtered organ suspen- 
sion. The virus is present in all affected organs, but the infective 
properties of these organs are lost in a few days after death. 
There are three principal theories as to the etiology of the dis- 
ease in man which are reflected by various writers in the interpre- 
tation of lesions in the fowl: 1. The lesions of leukemia are a 
simple hyperplasia. 2. Leukemia is a neoplasm. (See lymphoma). 
3. Leukemia is a result of the multiplication of an infective agent. 
146 
