Let us now examine the Table (2) according to orders and then as to causation. The Primates’ heart is apparently well able to increase in size in response to increased work, a demand most often made by pulmonary, pleural and pericardial diseases. Two of these cases occurred in animals suffering with pulmonary tuberculosis sufficiently extensive to impede cardiac action while in another case the tuberculous lesion was mild but a pericarditis existed. When the right hand columns are inspected it would seem that on occasion dilatation may occur; one of the tuberculous pulmonary cases had a dilated heart. The slothful lemurs apparently have no call upon their cardiac mechanism. Carnivora with their large organ, which, it would seem, should be prepared for excess work either simply as a reserve or as an inherent ability to grow, present in about equal numbers, hypertrophy and dilatation. It is admitted that there are within this order, genera of differing habits, but analysis of the canidæ, felidæ and ursidæ for examples, in the first place, offer too few specimens for conclusions and, secondly, have upon trial actually shown nothing definite, so that we are forced to use the larger group, the order. It is interesting to note that long continued infection is in this order the most potent factor in enlargements of the heart. Four of the ten cases show myocarditis. Nephritis does not seem very important in relation to cardiac muscular increase, but occurs with great frequency in association with dilatation. Three of the cases of hypertrophy were associated with thyroid disease and two of these showed dilatation as well. The general causes of chamber distention are more diverse, and we see associations that do not appear with hypertrophy, namely arteriosclerosis and diseases of the chest. TABLE 2. _Table Showing Incidence per Order of Hypertrophy and Dilatation, and the Principal Associated Lesions Believed to Have Etiological Importance._