870 Leukemia of Mammals. 



the blood of an infected dog was also unsuceessfnl (Stockmann). 

 On the other hand the infectious nature of chicken leukemia 

 (see p. 877) should be considered as proven, and in addition 

 several observations are known in human medicine, which in- 

 dicate the transmissibility of leukemia to healthy man (EUer- 

 mann & Bang). 



Lowit claims to have found protozoa (Haemomoeba leukaemiae) in the white 

 blood corpuscles of man affected with rnyelogenous leukemia, with which he suc- 

 ceeded in producing a marked leucocytosis in animals, but without an affection of 

 the blood-forming organs. Protozoa (H. leukaemiae vivax) were demonstrable in 

 the blood-forming organs of lymphatic leukemia. Other authors have not substan- 

 tiated this finding and consider the bodies observed by Lowit as fragments of cells. 

 Pawlowsky found bacilli in leukemic blood, with which he failed, however, to pro- 

 duce the disease. Likewise negative were the attempts at inoculation of rami, 

 Delbet and Lucet. 



Pathogenesis. Ehrlich's thorough hematological examina- 

 tions have thrown some light on the development of the disease. 

 According to these, the hyperplasia of the lymphadenoid tissues 

 develops in some cases under the influence of a still unknown 

 cause, whereby the blood becomes flooded with the lymphocytes 

 which are formed in much greater numbers (Leukaemia lymph- 

 atica), whereas the number of true leucocytes remains un- 

 changed. The hyperplasia of the lymphadenoid tissue affects 

 not alone the lymph glands, but also the spleen, the bone marrow, 

 the intestinal wall, and usually also other organs (liver, lungs, 

 kidneys, glands, etc.), which under normal conditions contain 

 only microscopically small lymph follicles. Exceptionally how- 

 ever the hyperplasia of the lymphadenoid tissues occurs only 

 in a few, or even only in a single organ (for instance in the 

 bone marrow). 



In other cases of leukemia the causative factor effects a 

 proliferation of the myeloid tissue, when the leucocytes migrate 

 from the blood stream in great numbers, at the same time how- 

 ever young unripe leucocytes as well as numerous ripe leucocytes 

 migrate from the leucocyte-forming bone marrow, and flood 

 the blood (Leukaemia myelogenes [s. myeloides]). Besides the 

 bone marrow, other blood forming organs also become affected, 

 more particularly a hyperplasia of the spleen, lymph glands, 

 liver, and the development of areas of tissue-like bone marrow 

 results in these organs. 



This classification of the forms of leukemia by Ehrlieh ap- 

 pears, considering the morphology of the white blood cor- 

 puscles, much more appropriate than the designation of 

 leukemia in accordance with the blood-forming organs, which 

 are found alone or most strikingly affected on macroscopical 

 examination, as on one hand all blood-forming organs are in 

 most cases more or less affected in both forms of leukemia, 

 while on the other hand the lymphatic and the myelogenic 

 leukemia probably represent even etiologically two different 

 diseases. As the white blood corpuscles formed in the spleen 

 do not appear to have any part in the leukemic cases of 



