Struthiones │ │ │ │ │ │ Crypturi │ │ │ │ │ │ Total Birds │ 1│ 2│ 1│ 5│ 0│ 3 ─────────────┼─────────┼───────┼─────────┼─────────┼───────┼────────── Total │ 9│ 14│ 8│ 16│ 3│ 13 ─────────────┴─────────┴───────┴─────────┴─────────┴───────┴────────── For meaning of italics see foot note Table 1. The rodents seem to have no power to increase muscle bulk, but a sufficient number of cases of dilatation occur to make one conclude that this is their method of response to unusual strain. Pulmonary disease, mostly of infectious nature, and myocardial degenerations are the principal causes. The next order to show cardiac enlargement is the Ungulata where nephritis is the most frequent association with hypertrophy and disease of the pleura and pericardium with dilatation, or the reverse of the factor value in the Carnivora. These animals, fairly well prepared for flight, with moderately large hearts, seem more often to show dilatation than hypertrophy. Two Edentata (armadillo) showed dilatation but no hypertrophy. Marsupials behave somewhat like rodents in that the heart does not seem to increase muscle bulk, but our records do not explain this clearly. As already mentioned four cases had no sufficient internal reason for dilatation, but as one was probably the result of shock three only remain to be accounted for. Nephritis seemed to exist in all three, but two of them had kangaroo mycosis of the jaw and a general chronic infection. If now our attention be given to the Aves we find the highly specialized Passeres and Striges not represented and their closely related well- organized orders Picariæ and Psittaci with only an isolated single case. This is the more interesting since the last order suffers reasonably often with arteriosclerosis. Accipitres, the birds of pugnacious habit and carnivorous diet, seem well able to increase their muscle upon demand, but do not often suffer dilatation. Vascular and renal diseases stand out most prominently in the etiology, and one-half of them show myocardial change. The Galli, which includes both ground and flying birds, are represented but fail to exhibit any unusual accompanying disease. Anserine birds apparently have a low power to increase the size of the heart, but most often allow it to dilate. Struthiones, large stalking and rapidly travelling birds, apparently have a good margin of safety in their cardiac mechanism. SUMMARY OF LESIONS ASSOCIATED WITH HYPERTROPHY AND DILATATION.