64 VETEKINAEY PHYSIOLOGY 



element of a battery, the zinc ; the uncontracting part to the 

 negative element, and the wire coming from the contracting 

 part will, therefore, correspond to the negative pole that from 

 the uncontracting part to the positive pole. 



It has now been shown that this current of action occurs 

 along with, and does not precede, the period of contraction. 

 The electric change in contracting muscle may be demonstrated 

 by laying the nerve of one muscle-nerve preparation over the 

 muscle of another muscle-nerve preparation or over the beating 

 heart, when it will be found that the first muscle contracts with 

 each contraction of the second, being stimulated by the current 

 of action. (Practical Physiology.} 



VII. Extensibility of Muscle 



The extensibility of muscle is increased during contraction so 

 that the application of a weight causes a greater lengthening 

 than when the muscle is at rest. 



3. The Chemical Changes in Muscle and the 

 Source of the Energy evolved 



Chemical changes are constantly going on in muscle and 

 the study of these chemical changes in resting muscle and 

 in the contracting muscle explains the source of the energy of 

 muscle. Disintegration leads to the liberation of energy and 

 construction leads to the repair of the muscles and to the 

 storage of energy. 



No part of physiology is of more importance ; for it is the 

 chemical changes in muscle which give rise to the great 

 waste products of the body, and it is to make good these 

 losses that fresh nourishment has to be supplied. The 

 chemical changes in muscle therefore govern both the intake 

 and output of matter from the body. 



By studying the question from a number of different 

 standpoints, and by comparing the results so obtained, a 

 fairly clear conception of the chemical changes and the 

 source of muscular energy has been obtained. 



1. Composition of Muscle before and after Contraction. 

 The method which most naturally presents itself is .to take 



