GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 159 



made. Purely physiological phenomena are such as can be exhibited only 

 by a mechanism which has the chemical and physical structure of living 

 protoplasm, and such as cease with the life of the protoplasm. 



The electrical phenomena of nerve are capable of being divided into two 

 classes, the one, purely chemico-physical, resulting from the core-conductor- 

 like structure, and the other, physiological, intimately dependent on the reac- 

 tions of the living protoplasm. The medullated nerve is not merely a core- 

 conductor. 



It is too soon to try to separate these two classes of phenomena ; we must 

 wait not only for more work to be done on nerves, but on other irritable forms 

 of protoplasm, for many of these, although of entirely different structure from 

 the nerve, exhibit very similar electrical reactions. 



F. Chemistry of Muscle and Nerve. 

 I. Chemistry of Muscle. 



Muscles consist of muscle-fibres bound together by connective tissue. 

 Between the fibres we find nerves, blood-vessels, and lymphatics. Fat-cells 

 containing considerable fat may also be found in the midst of the connective- 

 tissue network. Each fibre consists of a sheath, the sarcolemma, which 

 resembles elastin in its constitution, and within this the muscle-substance 

 proper, together with certain substances of nutritive value and waste prod- 

 ucts. 



Muscle which has been freed as far as possible from blood, connective 

 tissue, and fat, has a mean specific gravity of 1.060; the extreme variations 

 found for the muscles of different animals being 1.053-1. 074. l When it is 

 fresh the reaction is slightly alkaline. 



It contains about 75 parts of water and 25 parts of solids; nearly '_'<> 

 parts of the solids are proteids, the remaining 5 parts consisting of fats, ex- 

 tractives, and salts. 



Little is known concerning the chemistry of living muscle; the instability 

 of the complex molecules which make- possible the rapid development of energy 

 peculiar to muscles renders exact analysis impossible. The manipulations 

 essential to chemical analysis necessarily alter and kill the muscle protoplasm. 



Death of the muscle is ordinarily associated with a peculiar chemical change 

 known as rigor mortis. To understand the chemical composition of muscle it 

 is necessary that we should consider the nature of this change. 



1. Rigor Mortis. — Rigor mortis, the rigidity of death, is the result of a 

 chemical change in the substance of a muscle by which it is permanently 

 altered, its irritability and other vital properties being irretrievably lost. The 

 change is manifested bya loss of translucency, the muscle becoming opaque, and 

 by a gradual contraction, accompanied by a development of heal and acidity, 

 and resulting in the muscle being stiff and firm to the touch, less elastic, and 

 less extensible. Whenever muscle dies it undergoes this change. 

 M'arvallo and Weiss: Journal dc I'lu/sinlixjir, ls'.i'.i, i. p. 1204. 



