THE STUDY OF MUSCLE PHYSIOLOGY. 205 



under whicli they are manifested. It may be shown that every 

 one of the qualities which a muscle possesses varies with the 

 temperature, the blood-supply, the duration of its action, the 

 character of the stimulus, and other modifying agents. Not only 

 are there great variations for different groups of animals, but 

 lesser ones for individuals ; though the latter are made more 

 evident indirectly than when tested by the usual laboratory 

 methods ; but they must be taken account of if we would un- 

 derstand animals as they are. Some of these will be referred 

 to later. 



If a muscle-cell be regarded in the aspect that we are now 

 emphasizing, its study will tend to impress those fundamental 

 biological laws, the comprehension of which is of more impor- 

 tance than the acquisition of any number of facts, which, how- 

 ever interesting, can, when isolated, profit little. 



Summary of the Physiology of Muscle and Nerve. —The 

 movements of a muscle are distinguished from those of other 

 forms of protoplasm by their marked deflniteness and limit- 

 ation. 



The contraction of a muscle-fiber (cell) results in an increase 

 in its short transverse diameter, and a diminution of its long 

 diameter, without appreciable change in its total bulk. 



Muscle and nerve are not automatic, but are irritable. 

 Though muscle normally receives its stimulus through a nerve, 

 it possesses independent irritability. 



Stimuli may be mechanical, chemical, thermal, electrical, and 

 in the case of muscle, nervous ; and to be effective they must 

 be applied suddenly and last for a brief but appreciable time. 



Electrical stimulation, especially, is only effective when 

 there is a sudden change in the force or direction of the cur- 

 rents. This applies to both muscle and nerve. 



A muscular contraction consists of three phases : the latent 

 period, the period of rising, and the period of fallijag energy, or 

 of contraction and relaxation. 



When the phase of relaxation is minimal and that of con- 

 traction approaches continuity, a tetanus results. The contrac- 

 tions of the muscles in situ are tetanic, and are accompanied 

 by a low sound, evidence in itself of their vibratory character. 



The prolonged contraction of a muscle leads to fatigue ; 

 owing in part, at least, to the accumulation of waste-products 

 within the muscle which depress its energies. 



This is a necessary consequence of the fact that all proto-' 



