ROBERT VAN CITTERS 
5 
terest of a new group of researchers who are 
using the availability of the breeding colony to 
study such things as reproductive biology, 
mother-infant relationship, developmental ab- 
normalities, sudden infant death syndrome, 
and many other practical problems with a very 
obvious relationship to human welfare. The de- 
velopment of primate breeding colonies in con- 
junction with the primate centers provides the 
medical research community with a nearly ideal 
model for study. An animal model closely re- 
lated to man is now available for study through- 
out its entire biological range, from conception 
through geriatrics. The model is a known quan- 
tity and its genetics can be predetermined by 
scientific breeding, its behavior is documented, 
and, of course, its physical condition can be 
controlled. The primate center program repre- 
sents one of the great opportunities for the bio- 
medical research community and I hope that 
many researchers will look at primate species 
when designing experiments. 
Regardless of the nature of the experiment, 
the fundamental requirement is to incorporate 
the selection of an appropriate model as part of 
the experimental design. Very clearly the selec- 
tion of an animal model becomes a part of the 
experimental design. Clearly also, the burden is 
on the experimenter to justify his selection. I 
think one could go beyond that and recommend 
that the scientific journals require justifica- 
tion of the model and its authenticity, perhaps 
as a part of scientific review. 
In all of the foregoing remarks, I have 
used the cardiovascular system as an area of 
concern (and the mongrel dog as the whipping 
boy) primarily because this is the system to 
which most of the members of this group ad- 
dress themselves. But I think it would require 
no great imagination to identify other examples 
of suboptimal models in many other areas of 
study like atherosclerosis, behavior, cancer re- 
search, and so forth. 
There is a further opportunity to extend the 
application of animal models to clinical medicine 
through deliberate exploitation of the compara- 
tive approach. In the comparative approach, one 
performs what Scholander has called "experi- 
ments in nature" ; that is, one exploits an exag- 
gerated physiological Or pathological character- 
istic or phenomena exhibited by an animal 
species as a normal biological variation. One 
attempts to learn from such experiments certain 
clues which can be applicable to general proces- 
ses in animals or man. Relatively few research- 
ers have taken advantage of this opportunity, at 
least intentionally, but the results of the experi- 
ments of comparative physiologists and pathol- 
ogists have made very major contributions. Let 
me cite a few examples. 
The discovery of the squid giant axon pro- 
vided membrane investigators with a model for 
study which has led to significant advances in 
our understanding of neurophysiology. 
The giant muscle cell of the barnacle provides 
a model which will probably come to equal ad- 
vantage. We can learn other things from the 
barnacle as well. The barnacle secretes a ce- 
ment which will adhere to all manner of sur- 
faces and this would probably be of some inter- 
est to bioengineers or even dental researchers. 
The secretion of inert gases into the swim 
bladder of certain fishes is a physiological phe- 
nomenon which has obvious basic biological 
implications. 
The peculiar anatomy of the giraflfe makes a 
very interesting model for study of the cerebral 
circulation. The giraffe's brain is 8 feet or so 
above its heart and the hydrostatic equivalent 
of 8 feet is about 200 mm of mercury. So one 
can postulate that this animal has to have either 
essential hypertension or a very bad case of 
cerebral ischemia when he's standing up. Either 
of these is a very interesting possibility. But 
the possibilities are even more exciting when the 
giraffe bends down for a drink, or after drink- 
ing, when he raises his head very suddenly. All 
of these possibilities suggest that c-ome means 
exists for regulation of the cerebral circulation 
in the giraffe, and that the anatomical exag- 
geration peculiar to the giraffe is compensated 
for by equally exaggerated control systems 
which then could serve as a model for study. 
Some years ago Scholander became concerned 
over temperature regulation in whales. How 
does a whale maintain a core temperature of 37° 
C when its life cycle takes it through the tropics 
and down into the Antarctic waters where the 
temperature is around 0° C? It was obvious im- 
mediately that the tail fluke served as the radia- 
