Frequency and types of tumors in mammals and birds of the Philadelphia Zoological Garden.

The post mortem records of the Philadelphia Zoological Garden are continuous since 1901. Reviews of these records for each decade through 1931 have shown that the frequency and types of malignant tumors did not change appreciably during this period (7, 8, 17). The frequency for all taxonomic groups was generally proportional to longevity, which often had been limited by nutritional disease. The types and locations of the tumors were not unusual, except perhaps in certain groups of birds. During 1935 the traditional and often inadequate diets then common to zoological gardens were replaced in the Philadelphia Zoological Garden by controlled diets (I9, 20). Since then, the frequency of tumors has increased in animals of a number of taxonomic groups. The present review will determine whether this increase may be explained by increased longevity or whether other factors must be suggested. At the same time, we may also determine whether the types and locations of the more common tumors have changed with improved nutrition. This study will compare the records for 1901 to 1934 with those from 1935 to 1956, i.e., 33 years before and 21 years after diets were improved.