54 DISEASE IN WILD MAMMALS AND BIRDS 
are pearl gray or irregularly salted with a whitish granu- 
lar material so that they are entirely opaque ; occasionally 
the distribution is spotty. The deposit does not seem to 
penetrate the myocardium. There is at times some 
involvement of other serosae, but this is usually much less 
marked than around the heart. It does not seem that this 
of itself should be fatal, but it has been the most decided 
pathological factor in some of the autopsies. 
Aside from pericarditic exudates, twenty-one instances 
of pericardial effusion have been encountered. They offer 
little that is peculiar in etiology, chemistry or cytology, 
but as there has been some question of the position of the 
accumulation of the fluid in human beings, it might be 
well to note the position in our material. It is recognized 
in veterinary medicine that the cardiac dulhiess is 
increased especially to the right, and that most of the 
fluid will be on that side and posteriorly. At our 
autopsies on mammals this is the position usually occu- 
pied by the fluid, the apex being covered by pericardium, 
unless the quantity be great enough to make the sac taut, 
and this position is retained whether the animal be laid 
upon the one side or the other ; nor does the fluid all leave 
the base of the heart when the body is placed prone. The 
crowTi of the heart is nearly always well covered. In birds, 
on the other hand, the fluid occupies the apical part of the 
sac, probably due to the fact that this membrane is 
attached by its tip to the transverse air sac wall which 
takes the place of a diaphragm, so that the tip of the heart 
is always free and the pericardium of the base fairly 
closely applied to the epicardium. This holds good even 
for the birds whose cardiac apex is normally attached to 
the pericardium by a fibrous band. 
Hypertrophy and Dilatation. 
The response of the heart to a continued demand upon 
its working capacity will, as already indicated, lead to 
increased muscle bulk or to larger chamber size. Whether 
