66 - THE AMEEICAN MONTHLY [April, 



tine, is constructed out of columnar cells (only positively proven by sections 

 in at least two directions) , whose nuclei, the oval bodies, are placed deeply in 

 the cell near the basement membrane. Perhaps a lucky section may demon- 

 strate one of these cells clearly with its basement walls, side walls, and nucleus 

 even more clearly than as shown in fig. 3, but if it does not do so the suflS- 

 cient study of the appearances of the section will convince the observer that 

 the interpretation above given is the only one which will explain the actually 

 observed facts. The cells themselves, then, are the granular stained sub- 

 stance which is protoplasm ; the active working material with the nucleus, 

 also concerned in the activities of the mucous membrane and the walls, and 

 the work of the mucous membrane of the intestine, is actually parcelled out 

 to the different individual cells. 



One very noticeable feature of the cells of the mucous membrane in the in- 

 testine is the innumerable small intensely black ' specks ' seen in the outer ends 

 of the cells evei'y where, so constantly that the irresistible first impression would 

 be that they were a part of the cell as properly as any of the other recognized 

 parts. They are not, however, a necessary part of the cell, for it could doubt- 

 less perform its work as well in their absence. Their pi'esence interests the 

 general biologist very much, for they are solid bodies, and have been swallowed 

 by the cells from the contents of the intestine, though usually the food must be 

 made liquid before it can pass into the cells of the intestine and through them 

 to the blood. 



Over the mucous membrane of the intestine, throughout its entire length, a 

 thin unstaining hyaline (g)assv) band extends, figs, i, 2, 3, 4, c, called the cu- 

 ticle. The cuticle follows all the bends of the epithelium or mucous membrane, 

 and during life adheres to the outer ends of the cells. In sections, as, for in- 

 stance, in fig. 3, it may be detached and lie at a distance from the cells. The 

 most careful study of the cuticle fails to show in it a repetition of the facts 

 which prove the mucous membrane cellular, and we may state that it is made 

 by the solidification of a sort of slimy secretion poured out from the mucous 

 cells, hardening where it is poured out, instead of being removed as fast as 

 formed, as are other secretions. It would be interesting again, in a paper of 

 biological interest, to stop for the inquiry into the purpose of this cuticle, but 

 we must set that question aside. 



2. The circular muscle layer is much more difficult to study and under- 

 stand than the mucous membrane. First examination of cross sections will 

 show, bounding the entire section, as in figure 1, a narrow band faintly stained 

 and with a few deeply stained oval nuclei scattered at intervals through it. 

 These give some clue to the cells, because the nuclei are in the middle of the 

 cells of the layer. Prolonged examination of good sections will convince one 

 that the circular nuclei laN-er is penetrated by lines which run with the band. 

 These are faintly shown in the figure of our plate, but only very imperfectly. 

 In sections they will be seen as the walls of the cells, and the cell shape de- 

 termined to be that of a spindle, long and tapering at each extremity. Fur- 

 ther, the cells are placed side by side, and with their long dimension across the. 

 intestine cross-section of the cells, which are, you will see, longitudinal sec- 

 tions of the intestine, present the circular layer with a very different look. 

 They are not now seen as long, tapering bodies, but as a row of deeply stained 

 nuclei in a band of faintly stained dots. This is because the narrow, tapering 

 cells, cut endwise, are reduced to scarcely more than points of usually less size 

 than the nuclei because of the taper, a few only being cut through their mid- 

 dle, and because the protoplasm through the cell at large stains less deeply 

 than the protoplasm of the nucleus. The circular muscular layer is composed 

 of cells, which are like the cells in the two layers in the intestines of verte- 

 brates, and known there as unstriped or involuntary muscle. 



