6 Harry C. Schmeisser. 
conclude, therefore, that a cell-free filtrate is effective and that the 
cause must be an organized virus. 
In the same year, Ellermann and Bang” reported that the blood of 
leukemic fowls contained the virus. They also showed that among 
transmitted cases the disease may appear as a typical leukemia or as 
a pseudoleukemia, or only as an anemia with changes in the bone- 
marrow. The injection of five animals with a Berkefeld filtrate re- 
sulted in one early leukemia. The injected fowls were isolated and 
great care was exercised during the experiment. 
The following year, 1909, Ellermann and Bang,” reported the 
transmission of the disease into the sixth generation, and also an addi- 
tional positive Berkefeld filtrate series. Because the disease can be 
produced by a cell-free filtrate, they conclude: (a) Leukemia must 
be an infectious disease; (b) it is to be placed among the diseases due 
to a filterable virus. They call attention to the fact that mitoses in 
the blood are pathological and always present in leukemia. 
Schriddle,* in 1909, was the first to question whether, in leukemia, 
we are really dealing with an infectious etiology. Basing his con- 
clusions upon experimental work, he claims that chickens, injected 
with extracts of entirely normal organs, present the same changes 
as Ellermann and Bang have reported for leukemia. He thinks that 
their findings are not leukemic and that, therefore, there is no proof 
in favor of the infectious etiology of this disease. 
Hirschfeld and Jacoby” in 1909, report a spontaneous case of 
leukemia showing changes in the blood and organs which, they claim, 
agree entirely with the description of Ellermann and Bang. In a 
second case, the blood picture, although not typical, appeared to 
them leukemic. At autopsy this fowl showed a typical chicken tuber- 
culosis. They succeeded in transmitting this tuberculosis, in asso- 
ciation with the apparently leukemic blood picture, into the fourth 
generation. They did not know whether they were dealing with 
a combination of tuberculosis and leukemia in the same animal, or 
with pure tuberculosis. An animal injected with a pure culture of 
the chicken tubercle bacillus developed a blood picture identical with 
that of the second spontaneous case. Therefore it seems highly prob- 
able that this case may have been one of pure tuberculosis. At any 
rate, it cannot be accepted as a definite and pure case of leukemia. 
The following year (1910) the same authors “ report the injection 
of fowls subcutaneously from their first spontaneous case. They 
