The Hearts of Wild Animals in Captivity.

Comparative anatomical studies of the heart in various mammals, with reference especially to the relation of the heart weight to the body weight, have yielded much interesting information. It was shown previously 1 that the heart of the racing greyhound averaged 13.8 gm. per kilo of body weight and stood at the top of the animal series in respect to relative heart size. It was also found that even the young greyhounds who had been confined to small kennels had relatively large hearts. Similar conditions but less striking figures were found in the study of the heart of the thoroughbred race horse 2 in which the average of 8.65 gm. of heart per kilo of body weight would indicate a similar change. This enlargement of the heart was present also in the young horses, colts and yearlings. The seasoned racers in both series had relatively enormous hearts. It was suggested that there was perhaps an inheritance of this acquired characteristic in the enlarged heart which had the capacity for even greater enlargement under stress. The factor of selection in breeding, however, was considered probable as a most potent factor. The greyhound heart averaged 5 gm. per kilo higher than did the heart of the ordinary dog, 13.8 as contrasted to 7.98. The thoroughbred's heart averaged about 2 gm. more per kilo than the ordinary horse's heart, 8.76 as contrasted to 6.77.

Opportunity was afforded for pursuing comparative anatomical heart weight-body weight studies on the animals that had to be sacrificed or died in the zoo, and thus was added interesting information on the question of the relation of heart weight to activity from another point of view.