10 THE AMERICAN MONTHLY [January, 



have all contracted. In like manner the muscular coat of the small 

 intestine causes the peristaltic actions, because the circularly-placed 

 cells contract in regular succession from front to back, pushing the con- 

 tents along before the progressing constriction, and the longitudinally- 

 placed cells, by their contraction after the circular ones, draw the 

 constricted part to its previous larger diameter. 



A person might ask why the muscles should do this ; how are they 

 advantaged.'' Now, in the first place, we should answer that we are 

 not sure that all cells must be advantaged in the body as a whole, though 

 it is not at all sure that any are not ; and in the second place, we would 

 say that these cells in return for the work they do are abundantly sup- 

 plied with food ; for innumerable capillary blood-vessels keep these 

 cells constantly supplied with food and oxygen, and carry away their 

 waste products. To be sure their independence is gone, and they are 

 held in subjection like galley-slaves and must work when the order 

 comes, but in this respect they are not worse otl^ than people in other 

 societies. They have their periods of rest and are not in danger of 

 starvation if they don't happen to find food. It seems reasonable, then, 

 to regard the unstriped muscle cell as being benefitted by its position in 

 the colony, as well as being a helper in the colony as a whole. 



The striped muscle tissue is capable of being regarded in the same 

 way. Here the cells are less evident, and we have to go back to their 

 history and trace their development to find them, for they are peculiarly 

 modified. Single elongate cells* multiply the nuclei remaining in one 

 family and surrounded by one envelope, the sarcolemma. The proto- 

 plasm of the cells, besides surrounding the nuclei, spreads out in the 

 form of a fine network in which lies the peculiar contractile substance, 

 which has a very perfectly arranged structure and is capable of very 

 quick and definite performance. The muscle tissue is made up of 

 fibres which are thus derived from cells, and the contractile substance is 

 a special substance made by the general protoplasm and built up in a 

 very definite way. The unstriped tissue is thus much more evidently 

 cellular than the striped tissue. But not only the derivation of the 

 striped cells, but also the striped structure of the spindle-shaped cells 

 of certain lower anilnals, e. g.^ the disco-medusa, and the presence of 

 the nuclei on the side walls of the fibres, go to show the cellular nature 

 of the striped muscle fibre. The striped tissue is much more rapid 

 and precise in its work, and this is plainly correlated with its much 

 higher specialization of the contractile substance. If it is difficult to 

 understand the ultimate nature of the muscular contraction, so it is in 

 the simplest mass of protoplasm which moves at all, and if we could 

 understand fully the motion of a flagellum of any monad we should 

 have the factors needed to solve the problem of the simple muscular con- 

 traction. 



Given the striped muscular tissue as a cellular aggregate, and the 

 actions of the tissue as to its use in various parts of the body are not 

 difficult to understand. The biceps flexes the elbow joint, because 

 its fibres are placed lengthwise, and all contracting together, pull on 

 the tendon, and tlie joint follows and is bent. The sartorius lifts the 

 knee because of the relations of the muscles and bones and the shortening 

 ot the fibres. Even the voice of the frog is a special case of muscular 



*See Hatscheck Lehrbuch der Zoologie, p. 125. 



