LEUKEMIA 323 



found, or variations and degrees of either of the two forms 

 may be present. 



Occurrence.— This disease occurs most frequently in dogs, 

 occasionally in cats. 



Etiology.— Nothing is definitely proved relative to the 

 cause of leukemia. The disease is probably of an infectious 

 origin, but experiments conducted along this line have given 

 negative results. Toxic agents have been given as the 

 cause, as have injuries and various other factors. 



Pathology.— On necropsy in leukemia it is often difficult 

 to make a distinction between the two forms as' the lesions 

 of both occur concomitantly in the majority of cases. It is 

 characterized by enlargement of the spleen, lymph glands, 

 liver, kidneys and distinct changes in the marrow of the 

 bones. 



The spleen is enlarged (in some instances three to four 

 times its normal size), dense and often easily torn. Fre- 

 quently nodules are seen projecting from its surface. The 

 color is dark red, and on cut surface dry, and shows numer- 

 ous whitish colored, enlarged follicles each of about the size 

 of a wheat grain. The stroma of the gland and the capsule 

 are thickened. 



The lymph glands are found enlarged. They are harder 

 or softer than normal, of a whitish or gray color, sometimes 

 showing small red points over a cut surface. The surface 

 when scraped gives off a yellowish, creamy material. The 

 majority of lymph glands will be found affected. The bone- 

 marrow is of a dark red or gray color, and soft consistency. 

 On examination the bone-marrow will be found very rich in 

 white corpuscles. 



The liver is enlarged and shows numerous small nodules 

 of lymphoid tissue. The kidneys are enlarged in the same 

 manner. Small nodes will be found throughout the serous 

 membranes, lungs and other tissues in the body. 



Symptoms.— The early development of leukemia is usually 

 not observed. Very often the disease is not recognized until 

 the symptoms become prominent and it has reached the 

 advanced stage. The early symptoms are very similar to 

 those of anemia, and the differential diagnosis may be very 



