GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 67 



individual muscle : fiber is penetrated near its center by the nerve 

 where it terminates ; the ends being practically free from nerve in- 

 fluence. ^The stimulus that comes to the muscle-fiber acts primarily 

 upon its center, the effect of which then travels in both directions 

 to the endsvV^The manner in which the nerve-fibers terminate in 

 muscle will be more fully described in connection with the histology 

 of the nerve tissue. 



CHEMIC COMPOSITION OF MUSCLE. 



The chemic composition of living muscle is but imperfectly under- 

 stood owing to the fact that shortly after death some of its constituents 

 undergo a spontaneous coagulation and for the reason that the 

 methods employed for analysis also tend to alter its composition. 

 To human muscle, the following average percentage composition has 

 been given : 



Water, 73.5 



Proteids, including those of sarcolemma, connective- 

 tissue, pigments, 18.02 



Gelatin, 1.99 



Fat, 2.27 



Extractives, L 0.22 



Inorganic salts, 3-i 2 - (Halliburton.) 



(The composition of muscles of different animals, consumed as 

 foods, will be found in the chapter on Foods.) 



When fresh muscle is freed from fat and connective tissue, frozen, 

 rubbed up in a mortar, and expressed through linen, a slightly yellow 

 syrupy alkaline or neutral liquid is obtained which has been termed 

 muscle-plasma. This fluid at normal temperatures coagulates 

 spontaneously, the phenomena resembling in many respects those 

 observed in the coagulation of blood-plasma. The coagulum subse- 

 quently contracts and squeezes out an JickL jnuscle-seruno^Thfe 

 coagulated proteid is known as myosin and Belongs to the class t5f 

 globulins. Inasmuch as it is not present in living muscle and only 

 makes its appearance under conditions not strictly physiologic, it is 

 regarded as a derivative of a pre-existing proteid which has been 

 termed myosinogen. According to Halliburton, the proteids of living 

 muscle are four in number, distinguished by their varying solubilities 

 in different salts and by the varying temperatures at which they 

 coagulate. From muscle-plasma may then be obtained: (i) Para- 

 myosinogen and (2) myosinogen, the former coagulating at 47 C., the 

 latter at 56 C. It is myosinogen which is converted into myosin 

 under the influence of some special ferment, though both enter into 

 the formation of the muscle-clot. From the muscle-serum may also 

 be obtained at 68 C. a globulin body termed myoglobulin and a 

 small quantity of myoalbumin. Among the proteids may be men- 



