1 d4 The Lymphocyte and Lymphocytic Tissue 



Rodents 



Lymphocytic malignancies are infrequent but have been reported in the 

 rat 21 " and, of course, have been studied a great deal in the mouse. It is also 

 rare as a spontaneous disease in hamsters and guinea pigs. 



Monkeys 



We have been unable to find a satisfactorily documented case of malig- 

 nant lymphoma in a subhuman primate. It would be strange, indeed, how- 

 ever, if these species were not susceptible. 



Cattle 



Lymphocytic malignancies in bovine species are not infrequent; the 

 disease is world-wide in distribution and enzootic outbreaks have been re- 

 ported. In general, the disease in cattle is not particularly well documented, 

 although good descriptions of outbreaks and individual cases have appeared 

 in the literature. The disease is characterized by generalized invasion of 

 lymph nodes by malignant lymphoid cells which frequently infiltrate the 

 cardiac muscle.- 5 Acute forms of lymphocytic leukemia are sometimes seen 

 in young calves. Intense study of the disease in this species is definitely indi- 

 cated and should be fruitful. It is hoped that certain studies now getting 

 underway will yield information of value toward better understanding of 

 the disease. 



Of interest is the recent study by Barnes 1 of the records of the United 

 States Department of Agriculture relative to the incidence of lymphoma in 

 cattle slaughtered for food in establishments under the meat inspection 

 service of the Department. It must be borne in mind that these records 

 were not accumulated in order to study lymphoma, and the diagnoses were 

 made for the most part upon gross examination of slaughtered animals in 

 determining their fitness for human consumption. Nevertheless, the figures 

 accumulated are of interest in relation to the probable incidence of the 

 disease in cattle. According to these records, 230,170,948 cattle were slaugh- 

 tered during the years 1944 through 1958, and lymphoma was recognized in 

 27,7f)l of these animals. Between the years 1944 and 1953, malignant lym- 

 phoma was recorded at an annual rate per thousand slaughtered animals of 

 from 9.0 to 11.5. During subsequent years, 1954 through 1958, this rate 

 rose steadily to reach 18.0 per thousand. If these records reflect the true 

 status of the disease in cattle in this country, the incidence has been steadily 

 increasing since 1953, and the 1958 rate is twice that of 1944. Research is 

 definitely needed to evaluate this bovine disease by all means possible, to 

 determine if this apparent increased incidence is real, and, if possible, to 

 learn its causes. 



