398 TRANSMISSION 



and complicated than those semi-mechanical acts connected with 

 the deposition of eggs and the care of young, which are them- 

 selves in their essence not far removed from vital processes. 



All motion is reducible to irritability and contractility of 

 protoplasm as its ultimate cause, and any impulse that will pro- 

 duce this effect will lead to action. Furthermore, this action 

 must, from the nature of the case, be characteristic of the 

 organism and its peculiar mechanism. 



It has been held that all muscular activity must have its origin 

 in a nerve stimulus of some sort. That this is erroneous is self- 

 evident. Muscle tissue, unsupplied with nerve, is still contract- 

 ile, and the impulse can still be supplied from a variety of 

 sources (heat, light, electricity, contact). 



Nervous impulse is but one out of many stimuli to muscular 

 contraction, or other activity of living protoplasm, though it is 

 the most rapid and direct, and the one most readily under con- 

 trol of the mind and the will. Restating the proposition, nervous 

 mechanism is not necessary to motion, not even to coordinated 

 'motion of a high degree, but it is necessary to the highest coor- 

 dination of the most complicated organisms ; it is necessary as 

 the means by which the will may quickly reach all parts of the 

 machine and direct or set aside mere instinctive motion ; it is 

 necessary for the realization of all the possibilities of which a 

 highly organized structure is capable ; it is not necessary to 

 action, or even to a high degree of complication in action. 



Any effective impulse will serve to stimulate to activity ; 

 and, in general with all complicated actions, each act becomes 

 the impulse for the next. If the heart of a frog be cut into sev- 

 eral pieces these will all beat rhythmically, " but the number of 

 contractions will vary in the different pieces. The sinus venosus 

 beats most rapidly, and the number of its contractions in a unit 

 of time equals that of the heart before it was divided. Thus we 

 see that the whole heart beats in the rhy.thm of the part that lias 

 the maximum number of contractions per minute. From this we 

 must assume that the coordination of the htarfs activity is due to 

 the fact that the part which contracts most frequently forces the 

 other parts to contract in the same rhytJim" 1 



1 Loeb, Physiology of the Brain, p. 25. 



