DISEASES OF THE HEART 59 
often with arteriosclerosis. Accipitres, the birds of pug- 
nacious 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. Strutlii- 
ones, 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. 
Analysis of the associated pathology will reveal that 
among the mammals, renal disease, chronic infections 
and diseases of the thoracic serosa are most often respon- 
sible for hypertrophy, and that something over one-third 
of the hearts showed myocardial damage. Among the 
Aves arteriosclerosis and renal disease are most impor- 
tant in enlarging the heart; half of the cases had 
myocarditis. In so far as dilatation in mammals is 
concerned, renal disease and acute infections are decid- 
edly more important than other influences, even than the 
next in order — chronic infections and pulmonary dis- 
eases ; only one-fifth of the cases had myocardial disease. 
Acute infectious disease is the most potent cause of dilata- 
tion in birds ; only two of the eight cases had degeneration 
of the heart muscle. 
Comparison of Mammalia and Aves. 
If a comparison of the incidence of increased muscle 
bulk in the two classes be made (4) it will be found to 
occur two and one-half times more often in mammals, 
(4) This is done by determining the percentages of hypertrophy and 
dilatation for the total number of each class examined at autopsy. 
