ANNUAL ADDRESS OF THE PRESIDENT. XLV 
larger body, but the whole of the imparted motion is transmuted 
into heat or some other melecular motion. 
This law, that motion passes in the direction of least résistance, 
is the equivalent of the law of adaptation in the evolution of mat- 
ter. When evolution is considered from the standpoint of matter, 
it is convenient to use the term Adaptation ; when considered from 
the standpoint of motion, it is more convenient to use the term Least 
Resistance. 
EVOLUTION IN THE BIOTIC KINGDOM. 
In biotic bodies it has been seen that change is the result of in- 
ternal as well as external conditions. As external conditions, or the 
environment, are changing, these bodies change to a limited extent, 
in the same manner as do mineral bodies; but there is also a change 
brought about indirectly by the environment, through certain in- 
ternal changes in the constitution of biotic bodies. Through this 
internal constitution individuals are changed in time—one genera- 
tion dies and another succeeds. 
There is yet another method of change in biotic bodies, which 
steadily increases from the lowest to the highest—that is, the change 
in their constituent matter. While structure changes slowly from 
birth through growth and decadence to death, the constituent matter 
changes with much greater rapidity. In this change the minute 
elements of structure change much more rapidly than the larger 
into which they are compounded ; so that every part of the organ 
must be supplied with new material to replace that which is steadily 
becoming effete and passing away. Now the rate of this change in 
any integral part of an organism is dependent upon the activity of 
the organ. Exercise increases the rate of change in the constituent 
matter of a biotic organ, and thus the slow change in its structure, 
which proceeds from life to death, is accelerated. This accelerated 
change results in increased differentiation of the organ, and it thereby 
becomes more and more efficient in the performance of its function. 
This change, therefore, results from exercise. Organs that are ex- 
ercised increase in efficiency, by non-exercise they decrease in effi- 
ciency. This change in the organization of any one individual is 
but slight, but as the slight changes pass from one generation to’ 
another, continuous exercise of one set of organs greatly modifies 
them; continuous neglect of exercise in another set modifies them 
also, until at last they are atrophied. Thus by exercise and non- 
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