52 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



fiber. It has been pointed out,* for instance, that in frogs' muscles 

 three different proteins are known to be present, with three dif- 

 ferent temperatures of heat coagulation, namely, myogen fibrin, 

 35 to 40 C. ; myosin, 47 to 50 C. ; and myogen, 58 to 65 C v and 

 that when the living muscle is heated what is ordinarily designated 

 as the contraction of heat rigor comes on at the first temperature, 

 35 to 40 C., while small additional contractions occur at the 

 temperatures of coagulation of the other two proteins. This view, 

 however, does not make clear why the first of these coagulations, 

 that of myogen fibrin at 40, should produce such a large contrac- 

 tion, 80 to 90 per cent, of the total shortening, although this protein 

 is present in smaller quantities than the other two. As long, how- 

 ever, as it remains uncertain whether or not the shortening and 

 the coagulation are necessary features of death stiffening, it seems 

 premature to speculate upon the identity or difference between 

 the coagulation and shortening caused by death and the similar 

 phenomenon caused by high temperatures. 



PLAIN OR LONG STRIATED MUSCULAR TISSUE. 



Occurrence and Innervation. Plain or long striated muscular 

 tissue occurs in the walls of all the so-called hollow viscera of 

 the body, such as the arteries and veins, the alimentary canal, 

 the genital and urinary organs, the bronchi, etc., and in other 

 special localities, such as the intrinsic muscles of the eyeball, the 

 muscles attached to the hair follicles, etc. In structure it differs 

 fundamentally from cross-striated muscle, in that it occurs in the 

 form of relatively minute cells, each with a single nucleus, which 

 are united to form, in most cases, muscular membranes constituting 

 a part of the walls of the hollow viscera. These muscle cells, in 

 most cases at least, are supplied with nerve fibers which originate 

 directly from the so-called sympathetic nerve cells, and only in- 

 directly, therefore, from the central nervous system. 



Speaking generally, the contractions of this tissue are removed 

 from the direct control of the will, being regulated by reflex and 

 usually unconscious stimulations from the central nervous system. 

 All the important movements of the internal organs, or, as they 

 are sometimes called, the organs of vegetative life, are effected 

 through the activity of this contractile tissue. From this stand- 

 point their function may be regarded as more important than that 

 of the mass of the voluntary musculature, since so far as the mere 

 maintenance of the life of the organism is concerned, the proper 

 action and co-ordination of the movements of the visceral organs 

 is at all times essential. 



* Brodie and Richardson, 'Philosophical Trans., Roy. Spc.," London, 

 1899, 191, p. 127; also Inagaki, 'Zeitschrift f. Biol.," 1906, xlviii., 313. 



