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1891.] Quantity and Dynamics of Animal Tissues. - 973 
on different representatives of the same species would require a 
knowledge of the age, food, and environments of the different 
animals dissected, and then we would have to proceed upon a 
supposition, probably never realized in nature, that all the subjects 
of the experiment varied together in the quantity and distribution 
of all their tissues. Obviously such a supposition would be 
purely artificial; and to insure all the conditions for the faithful 
execution of the experiment would require precautions so labored 
and extraordinary as to baffle the most skillful experimenter. 
But while itis impossible to obtain exact and absolutely reliable 
data which may serve as the basis of laws of specific develop- 
ment, yet there are certain general and approximate methods 
which may lead to very much the same end. Such data may be 
derived in part by observations of the outward contour as deter- 
mined by the plumpness or leanness of the animal. It is true 
that inferences based upon such observations may often be mis- 
leading, owing to our ignorance’ as to just what tissues produce 
the fullness or shrinkage in any given instance, and as to whether 
the same amount of shrinkage at different times is caused by the 
degeneration of the same or different tissues. Many valuable 
suggestions may be gleaned, however, from post-mortem examina- 
tions of typical cases. Such examinations, if found to be often 
confirmatory of previous conjectures, will tend to inspire confidence 
in our methods and results. There can be nothing more certain 
than that most mammals are subject to easily observable changes- 
in.their external contour from the time of their birth onward. 
Puppies and kittens, for example, are clumsy and thick-set when 
born, the latter being positively corpulent. As growth proceeds, 
however, the legs and body elongate, and the relative proportions of 
limbs and body are altered in a marked manner, the body becom- 
ing often quite lank. Quite the reverse happens to the calf and colt. 
They are very gaunt and long-legged, to begin with ; but grown 
cows and horses become decidedly thick and sometimes unwieldy. 
The muscles also change in form and relative dimensions. 
Changes like these are points of common remark in the human 
subject. Plump babyhood and childhood, spare youth, stout 
manhood, and weazen old age have all found place in familiar 
