148 THE AMERICAN MONTHLY [May, 



the deeper ends of the cells are in relation with the 

 blood supply while their opposite ends open on the lu- 

 men. This is exactly the relation of cell and vessels in 

 all glands, and it enables them to work to the best ad- 

 vantage, for the cells can attract from the blood those 

 elements it shall use, and can throw oflF its products into 

 the lumen whence they are removed and thus their ac- 

 cumulation is avoided. At the bottom of the layer there 

 is a layer of muscular tissue, called the " muscularis 

 mucossD." The third coat of the organ is the usual mus- 

 cular coats this is composed of unstriped muscle tissue, a 

 fuller account of this tissue will be given and the cells 

 illustrated in connection with the small intestine. 



The small intestine, a tube in man thirty-nine feet 

 long and an inch in diameter, has a similar structure 

 throughout its entire length. The cut of vertical section 

 p. 149, will show the structure with sufficient clearness 

 for tlie purpose of interpreting sections made in an or- 

 dinary way. There are three coats, the two active coats, 

 muscular and mucus, and the accessory coats, sub- 

 mucous, in which the vascular and nervous trunks lie, 

 and from which they are distributed to the active layers. 

 The mucous coat on the inside is composed of a layer of 

 tubular glands, '^crypts," as in the wall of the stomach, 

 though the glands are not the same histologically as 

 those of the stomach, and in addition of a layer of 

 structures which are peculiar to this organ called "villi." 

 A little reflection on the fact^ shown in the figure will 

 show any one that a villus is the opposite of a tubular 

 gland ; a gland being a depression from the surface 

 which is lined with cells, while a villus is a projection 

 which is covered with cells. The difference is seen by a 

 consideration of the position of the blood-capillaries in 

 the two cases ; in the first, the capillary surrounds the 

 tube ; in the second it is inside, see fig. 1, p. 149. From 

 the point of view of the cell the relation is unchanged for 



