CHAPTER XV 



THE FUNCTIONS OF CROSS-STRIATED MUSCLES 



THE purpose of the cross-striated muscles is twofold : first to provide for 

 the bodily movements, and secondly to participate in the production and regu- 

 lation of heat in the body. In this chapter we shall first inquire into the 

 general properties of the muscles and shall then briefly discuss their relations 

 to other organs. 



FIEST SECTION 



GENERAL PHYSIOLOGY OF MUSCLE AND NERVE 



Inasmuch as the general properties of muscles and of nerve fibers agree 

 in many respects, and the information gained from nerves very often throws 

 light on the corresponding phenomena of muscles, it seems best to discuss 

 them here together. 



Physiologists have for a long time given preference to the study of the gen- 

 eral properties of muscles and nerves because at first it promised to yield very 

 important results bearing on the fundamental properties of the living substance 

 in general. A great number of facts have been collected by the work done in 

 this field, but unfortunately they do not as yet afford us a basis for any con- 

 sistent theory of nervous and muscular activity. Significant as these facts are, 

 we must be content to mention only the most important of them, a more exhaust- 

 ive presentation being quite beyond the possibilities of a text-book of this size. 



When not otherwise expressly stated, the facts given may be understood 

 as applying to the surviving nerves or muscles of the frog, exsected from the 

 body (cf. page 6). A motor nerve is generally employed in investigation 

 of the general properties of nerves, and in most cases the muscle connected 

 with it serves as the indicator of the state of the nerve. The changes in the 

 form of the muscle are usually registered by the graphic method (cf. page 6). 



1. FUNDAMENTAL LAWS OF NERVOUS ACTIVITY 1 



A nerve is irritable to ordinary artificial stimuli at all points of its course, 

 and it transmits the stimulus in both directions from the point of stimula- 

 tion. This is best shown by means of the action current (page 48). If a 

 nerve be stimulated at its middle, each of the two ends being at the same 



1 The properties of different kinds of nerve fibers will be discussed more fully in 

 Chapter XXII. 

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