264 



HISTOLOGY 



Epithelium. 



FIG. 258. FROM A SECTION OF THE SMALL INTESTINE FROM 



A KITTEN SEVEN DAYS OLD. X 250. 

 The epithelium on the left contains many wandering 



leucocytes (lymphocytes). The epithelium on the right 



contains but three. 



mitosis the nuclei move back to the basal layer. Lymphocytes which 

 have made their way between the epithelial cells (Fig. 256, b), are 

 frequently seen, and when near the lumen and over-stained they may be 

 mistaken for mitotic figures. 



The sides of the glands and surfaces of the villi are covered with simple 

 columnar epithelium, similar to that shown in Fig. 256. It contains 

 goblet cells separated from one another by cells free from mucus. The 



cells of the villi are taller than 

 those in the glands, and the 

 goblet cells are somewhat 

 larger, but toward the tip of 

 the villus they become slen- 

 der and empty (Fig. 257). 

 The top plates or cuticula 

 become thicker from the 

 fundus of the gland outward 

 to the tips of the villi, and 

 when well developed they 

 exhibit vertical striations which are considered to be protoplasmic 

 processes lodged in pores. The top-plate of the goblet cells is thin and 

 apparently ruptures to allow the escape of the mucus. Lymphocytes 

 may enter the epithelium in abundance as shown in Fig. 258. 



Interest in the villi centers chiefly in their relation to the absorption 

 of nutritive material from the intestinal contents (chyme). Fat, chem- 

 ically changed so that it does not 

 blacken with osmic acid, is con- 

 veyed through the cuticula. 

 Within the epithelial cells it forms 

 characteristic fat droplets, which 

 appear in abundance also between 

 the epithelial cells. Lymphocytes 

 ingest the droplets, and may then 

 enter the lymphatic vessel in the 

 central axis of the villus (Fig. 

 257), but apparently fat is con- 

 veyed to the lacteals also through intercellular spaces, without the inter- 

 vention of leucocytes. Within the lymphatic vessel it forms the milky 

 lymph known as chyle. 



In regard to the absorption of protein material, the observations of Pio Mingazzini, 

 which have been confirmed by some and denied by others, are of considerable interest. 

 As shown in Fig. 259, he found that the basal protoplasm of the resting epithelium 

 presented an ordinary appearance (A), but that after absorption had progressed, hya- 

 l ine spherules appeared iu it (B). As these became numerous they were detached from 



FIG. 259. STAGES OF INTESTINAL ABSORPTION AS 

 SEEN IN EPITHELIAL CELLS OF VILLI FROM A 

 HEN. (After Mingazzini.) 



A and D, The states of repose preceding and follow- 

 ing the process, s., Spherules. 



