THE TISSUES 67 



change increases the rapidity of the rhythm. Thus warming 

 the muscle and the action of a galvanic current have this 

 action. 



3. When the muscle is at rest, a contraction may be pro- 

 duced by any of the modes of stimulation which will cause 

 the skeletal muscles to contract ; and it may thus be demon- 

 strated that the latent period is very long. 



4. Unlike skeletal muscles, the extent of contraction is 

 not increased by increasing the strength of the stimulus. 

 The smallest available stimulus causes the maximum con- 

 traction; but if the same stimulus is repeated at regular 

 intervals the resulting contractions become greater and 

 greater during the application of the first four or five stimuli, 

 so that the record of a series of contractions has a somewhat 

 stair-like appearance. 



5. A series of stimuli do not cause a tetanus, but simply 

 increase the rapidity and force of the individual contractions. 



When the muscles are arranged round hollow viscera, the 

 rhythmic contraction, starting at one end, travels along the 

 group of muscle-fibres as a regular wave the peristaltic 

 wave and thus drives onwards the contents of the tube. 

 The rate at which this wave travels varies very considerably. 

 (Practical Physiology, Chap. IX.) 



Cardiac Muscle physiologically resembles other visceral 

 muscles, but its period of contraction is shorter and its 

 rhythm generally more rapid. 



4. THE CHEMICAL CHANGES IN MUSCLE AND THE 



SOUKCE OF THE ENERGY EVOLVED. 



Chemical changes are constantly going on in muscle, and 

 the study of these chemical changes in resting muscle and 

 in contracting muscle explains the source of the energy of 

 muscle, disintegration leading to the liberation of energy and 

 construction leading to the repair of the muscles and 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 



