DISEASES OF THE HEART 61 
compressed by the pressure of an excess of air in the 
pneumatic sacs. At all events while concentric hyper- 
trophy was mentioned once, it is difficult to estimate the 
degree of increase in the right chambers because they are 
not uncommonly well filled when diastole occurs at death. 
Grober (5) asserts that the normally large heart (or what 
I have called ''physiological hyperplasia") shows a 
''hypertrophy" of the right ventricle because of the extra 
work entailed in flying. This is certainly not the case in 
the material we have seen under pathological conditions. 
Eight-sided increase might be expected if pulmonary or 
serous membrane affections were prominent, but left- 
sided increase, following arteriosclerosis and nephritis is 
the actual finding. The best examples of concentric 
hypertrophy are in the dogs with thyroid disease and the 
best examples of concentric dilatation in ungulates 
suffering shock. 
Summary. 
The foregoing pathological data can now be sum- 
marized by grouping the facts under the headings of 
absolute and relative vulnerability of the heart. By the 
former is meant the actual number and quality of lesions 
in the various orders, but here at once one comes upon the 
irregularity of examples of zoological and pathological 
character, and if one trust entirely to the percentages, 
fallacious conclusions might be reached. Basing judg- 
ment upon the incidence of pathological lesions in 
mammals and birds, it is evident that the former has 
greater vulnerability, as 13 is to 6.2. This is noteworthy 
as we shall learn that the bird has a larger and appar- 
ently better prepared heart than the mammal. Attempts 
to discover the order or kind of animal having the great- 
est or lowest vulnerability are difficult for the reason 
given above. Thus, for instance, Pinnipedia, Probos- 
cidea, Edentata, Gaviae, Impennes, Steganopodes, and 
(5) Arch. fiir. Ges. Physiologie, 1908, 125, 507 
