TABLE 4. _Table Showing Weight of Normal Heart in Relation to Body Weight. Number of Specimens used to Determine Weight Quoted in Parenthesis._ ════════════════╤═══════════════════════════════ Average Heart of│Grams per Kilogram of Body.[12] ────────────────┼─────────────────────────────── Man ( 4)│ 5.67 Primates ( 4)│ 6.56 Carnivora ( 6)│ 6.78 Rodentia ( 5)│ 5. Ungulata (10)│ 5.8 Marsupialia ( 3)│ 5.1 │ Average 5.82 Passeres (43)│ 19.8 Picariæ ( 9)│ 21.3 Striges ( 4)│ 7.33 Psittaci ( 6)│ 8.89 Accipitres ( 7)│ 12.32 Columbæ ( 4)│ 14.47 Galli (16)│ 11.08 Fulicariæ ( 3)│ 23.82 Limicolæ ( 2)│ 8.78 Anseres (14)│ 11.8 Struthiones ( 1)│ 12.7 │ Average 13.84 ────────────────┴─────────────────────────────── For meaning of italics see foot note Table 1. However, there are many reasons why great caution should be used in evaluating the relative size of the heart. Welcher showed in his work that the proportion is greater in small and young animals than in large and adult ones. All the authors quoted agree that in birds and to less degree but still clearly in mammals, there is a direct relationship between the bodily activity of an animal and its cardiac bulk. This is fairly well shown in the list of avian heart ratios, but not so clearly in the mammals. What shall be considered the most active mammals—the monkey, perhaps, with his tendency to be occupied constantly, yet we find the greatest heart bulk among the Carnivora, animals prepared for travel and struggle, and the smallest among the Rodentia, quiet and timid animals. The avian order showing the greatest cardiac ratio, the Fulicariæ, shore birds, is made up of some quiet hiding varieties, and of some capable of very prolonged flight; the most constantly active fliers (Passeres) also have a high cardiac weight proportion. The inactive owls have the smallest heart bulk. The contrast between the average heart-to-body weights of mammals and birds is striking, the latter having two and one-half times as much as the former, 5.8 _vs._ 13.8. Since this is the most prominent and best supported statement in the table of weights, it may be used to compare with the incidence of the pathology as seen in the two classes. Degenerations and inflammations occur in mammals and birds as 9.5 is to 5.5.[13] Hypertrophies occur in mammals and birds as 10.3 is to 4.3.[13]