1871.] 255 [Cope. 
of these are supposed to be correlated to the Physical Forces, but are 
under direction and control of the Vital principle which locates their 
action, ete., just as molecular or atomic constitution determines the 
locality and character of the physical forces. The laws of the vital prin- 
ciple and of atomic constitution also determine the nature of the conver- 
sion of one force into another. Now, since physical and vital forces are 
correlated and convertible, the close relationship of the two controlling 
principles becomes obvious, and suggestive of their identity. 
Dr. Carpenter, in describing the correlation of physical and vital forces, 
defines the difference of organic species to be similar to that prevailing 
between different chemical bodiés (the latter depending on different mo- 
lecular and atomic constitution), which leads them ‘‘to behave differently” 
from each other under similar circumstances. This may be more fully 
expressed by saying that different species possess different capacities for 
the location of the conversion of the physical forces into growth-force. 
A “descent with modifications’? contemplated by a process of evolution, 
signifies a progressive change in this capacity. Acceleration means an 
increase in this capacity ; retardation a diminution of it. Grade influence 
means the influence which has produced this change of capacity. 
Precisely what the change consists in is a mystery, but that it is mat- 
erial in its character is rendered more probable the more we examine it. 
B. The Origin of Grade Influence. 
Living protoplasm can convert heat and nutriment into growth 
force without the agency of the nervous system. This is proven by the 
nutrition of the Protozoa and Celenterata and from experiments on the 
muscles of frogs, etc. In the latter case, as is well known, the nerve may 
be divided, and the muscle retain its size if a current of electricity be 
passed through it, thus sustaining the nutrition. As the presence and 
structure of the nervous system is in relation to the specialization of ani- 
mal structure in other respects, it is very probable that the nervous system 
is in higher animals the agent of the location of growth force. In the 
lowest it is not effected by any such means. As the nervous system is 
the instrument of the metaphysical peculiarities of the animal (emotions, 
choice, etc.), we may conclude that in the lower animals, location of 
growth force is influenced by necessity without choice; in the higher by 
necessity with choice. 
The impulses derived from the nervous system, it is known, may be 
reflex or automatic in consequence of application of stimuli from without. 
They may become so also, after having been originated consciously or by 
effort of will. In the case of habits, frequent exercise of choice has so im- 
pressed the nervous system as to result in its repetition of effort, often in 
opposition to changed choice. 
The influence of effort in muscular action on the nervous system ap- 
pears to be, first, to enable it to convert heat to nerve force, and, then, to 
conduct nerve force to the involuntary muscles or those controlling cir- 
culation, where it is converted into motion, which thus controls nutri- 
