Experimental Studies of Bovine Leukemia

Leukemia is essentially a blood disease in which there is more or less enlargement of the blood and lymph forming organs. There is usually a very marked increase in the number of white blood corpuscles with a possible decrease in the number of red cells. Leisering ^ is credited with being the first to demonstrate the presence of leukemia in animals in 1858, but from an investigational standpoint the disease received little attention until a much later date. Nocard, Mosler, Cadiot, Koger, Gilbert, Marek, Stockman, and a number of other European investigators have from time to time made studies of leukemia in animals, but it appears that comparatively little investigational work has been done on the disease in the United States. The various studies of leukemia in mammals have failed to reveal the etiological factor involved, and all efforts made to transmit the disease from animal to animal, through experimental inoculations or otherwise, have thus far given no definite results. On the other hand, certain Em*opean investigators have been able to transmit chicken leukemia through experimental inoculations, thus establishing the infectious nature of the disease in fowls. The present writers, however, have been unable to reproduce the disease in chickens by experimental inoculations of tissue emulsions from what appeared to be typical cases of avian leukemia. In dealing with the subject of leukemia it becomes necessary to differentiate between the true leukemia, in which there are very marked numerical changes in the cellular elements of the blood, and the so-called pseudoleukemia, in which the blood and lymph forming organs are similarly affected but without apparent changes in the cell content of the blood. It appears that leukemia is more rarely encountered, in some species of animals, at least, than pseudoleukemia. According to Ostertag,^ for example, pseudoleukemia is of more frequent occurrence in cattle and hogs than the true form of the disease.