Dila a A, 
NERES ES ME E VEI NEEE MIENO IEE a a el NG A E a tie eee dete 
1883.] Organic Physics. 139 
The life processes are not due to the single fact that oxidation 
of protoplasm yields unemployed energy. There is needed the 
secondary fact that protoplasm is so constituted as to make special 
use of this energy, by converting it into mass motion. Did it 
take only the general form of heat vibration, none of the phe- 
nomena of life could arise. We may reasonably ask, then, how 
does this conversion of free energy into mass motion take place, 
and what are its special conditions ? 
Fortunately we are not confined to the organic world for in- 
stances of this conversion. Similar phenomena occur in the in- 
organic world, and possibly the principle of action is in both 
cases the same. Parellels may readily be drawn between inor- 
ganic and organic motor activities, and a consideration of certain 
results of inorganic chemism may throw light on the phenomena 
of protoplasmic action. 
In considering the motor energies of protoplasm they appear 
partly indefinite and partly definite ; the former consisting of such 
motions as the streaming of protoplasm in plant cells, and the 
vague changes of form in the Rhizopods ; the latter of the higher 
animal “modes of motion.” The former is continuous, indefi- 
- Nite, general and seemingly purposeless; the latter is temporary, 
definite, local and with an evident purpose, Yeta close consid- 
eration of organic motions shows a connected series of steps be- 
tween the two phases indicated, and evidences of similarity in their 
instigating causes, which go to show that they are alike in origin 
and character. 
_ What is the source of the energy displayed in these motions? 
There is only one physical source apparent; namely, chemical 
change, In many instances chemical change evidently attends 
the Motions of protoplasm. This chemical change is an oxida- 
tion, and no such movement ever takes place unless oxygen be 
Ent Hence there is warrant for the assertion that all motion 
x protoplasm results from the action of motive force set free by 
Oxidation, and that for such motion to long continue there must 
be periods of rest from physical action, during which nutrient 
molecules can be assimilated, and a condition of ready suscepti- 
bility to oxidation reproduced. 
But there is an influencing cause of these motions, of essential 
'Mportance. This is the contact of external substance with the 
‘face of the protoplasmic mass. In nearly every case of animal 
