W. p. MCNULTY 
835 
our files. The leaflets of cardiac valves are said 
to thicken with age, microscopically showing 
an increase in loose connective tissue with mini- 
mal inflammatory infiltrate.** We have not sys- 
tematically examined the valves and cannot 
comment on this observation. At any rate, we 
have not seen calcification or deformities or 
associated signs of functional impairment in 
valves in the older of our animals. 
Myocarditis 
The myocardium of most macaques shows 
scattered small foci of accumulations of lymph- 
ocytes, histiocytes, and Anitschow myocytes 
(Fig. 11). Occasionally in these foci are a few 
necrotic muscle fibers. The cause and signifi- 
cance of these lesions is unknown. Necrosis can- 
not be a prominent feature, since focal scarring 
is uncommon. There is no associated cardiac de- 
compensation or hypertrophy, and the coronary 
arteries are normal or show minimal intimal 
thickening. 
The lymphocytic infiltrate brings viral in- 
fection to mind, but the prevalence, chronicity 
and focal distribution of the lesions weigh 
against this suggestion. Parasites have been 
looked for without success. 
The foci are faintly reminiscent of Aschoff 
bodies, and it is tempting to suspect an immune 
process. However, the ubiquity of the condition 
Figure 11. — Focal chronic myocarditis in an adult male 
rhesus monkey. H & E, 250x. 
and apparent lack of clinical significance are 
discouraging. Still, exploration with immuno- 
pathologic techniques might be fruitful. 
Hypertension 
Routine measurement of arterial blood pres- 
sure is not practical in large numbers of mon- 
keys and so the incidence of clinical hyperten- 
sion, or for that matter even the normal range 
of tension In unanesthetized animals, is not 
known. However, our postmortem records do 
not suggest that we are missing something. 
The hearts of 350 rhesus monkeys averaged 
from 0.6% of body weight at birth to 0.4% at 
maturity. The hearts of 20 of these weighed 
more than half again as much as expected, but 
none showed microscopic hypertrophy of myo- 
cardial fibers or interstitial scarring. No mon- 
key had hypertensive arteriolopathy, and 11 of 
the 20 were pregnant or had suffered recent 
weight loss. Hypertrophy of myocardial fibers 
has been described in chronically hypertensive 
rhesus monkeys," but measurements of weight 
and size of the heart were not given. 
Atherosclerosis 
This has been successfully induced by diet in 
several species of New and Old World monkeys.'' 
These diets, from the monkey's point of view, 
are bizarre; they contain high concentrations 
of cholesterol or lipids or both, concentrations 
much higher than those in laboratory chows or 
natural foods. The morphology of the lesions 
produced resembles that of the disease in man, 
especially in Old World monkeys and most 
particularly in chimpanzees. 
The rate of induction of experimental athero- 
sclerosis is much faster than the development of 
spontaneous human disease. This characteristic 
is enforced by the short span of investigators' 
attention and short duration of experimental 
projects, short, that is, with respect to the life- 
span of monkeys. Two important questions 
therefore require answers: (1) Is diet-induced 
atherosclerosis an acceleration and accentua- 
tion of the same process which would occur 
spontaneously, with much individual variation, 
on a "normal" diet? (2) If so, are methods which 
may be found to modify the evolution of rapidly 
