52 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



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. 



Distinctive Properties. The phenomena of contraction shown 

 by plain muscles are, in general, closely similar to those already 

 studied for striated muscle, the one great difference being the 

 much greater sluggishness of the changes. Plain muscles differ 

 among themselves, of course, as do the striated muscles, but, speak- 

 ing generally, the simple contractions of plain muscle have a very 

 long latent period that may be a hundred or five hundred times 

 as long as that of cross-striated muscle, and the phases of shortening 

 and of relaxation are also similarly prolonged; so that the whole 

 movement of contraction is relatively slow and gentle (see Fig. 

 25). Plain muscle responds to artificial stimuli, but the electrical 

 current is obviously a less adequate that is, a less normal stimulus 

 for this tissue than for the striped muscle. The amount of current 



