Comparative Pathology of Lymphocytic Malignancies 173 



the incidence has risen slightly from 2.14 to 2.5 per 1,000 admissions. 

 (About 8,000 dogs are admitted each year to this animal hospital.) It is 

 probable that this apparent increase in frequency of occurrence is not based 

 upon an actual higher incidence but rather upon the increased interest in 

 the disease and its more frequent recognition. (Reference is made to Fig. 

 13-12.) 



6 0- 



5 6- 



5.2 



4.8- 



4.4- 



4.0 



36- 



3.2- 



2.8 



2.4 



2.0 



1.6 - 



1.2 - 



8- 



4 



I I0JR 



948 I 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 



1948 1949 1950' 1951 1952 1953 1954 1955 1956 1957 1958 



Fig. 13-12. Annual rate per 1000 admissions of malignant lymphoma in 147 dogs and 

 98 cats. 



The age at which dogs may be affected with malignant lymphoma is 

 portrayed graphically in Figure 13-13. It will be seen that the disease occurs 

 in dogs from the first through the sixteenth year of age. The disease is seen 

 most frequently in dogs between the third and ninth years of age. Dogs in 

 this age group probably constitute the greatest segment of the canine popula- 

 tion. 



Cats 



The cat presents some interesting contrasts to the dog not only in tempera- 

 ment but in the way it is affected with malignant lymphoma. The distribu- 

 tion of the gross lesions differs particularly between these two species. The 

 presenting lesion in the largest group (20 per cent) of the feline cases is 



