FAT-ABSORBING FUNCTION OF ALIMENTARY TRACT OF KING SALMON. 165 



FAT-ABSORBING POWER OF THE SALMON INTESTINE. 



In the paper on the normal structure of the alimentary canal it has been shown that 

 the salmon intestine has a histological structure relatively simple. It possesses the 

 same epithelial lining coat, the tunica propria, the stratum compactum, and muscular 

 membranes which are found in its diverticula the ccEca. The mucous membrane itself 

 is shown to be somewhat more complexly folded than in the caca, a complexity that 

 increases with the size of the fish. No differentiations are found in the different por- 

 tions of the epithelial coat of the mucosa. Even in the deepest grooves or pits of 

 epithelium the cells have the same general form and structural characteristics as in the 

 most superficial folds. 



The intestinal epithelium of the salmon is also a fat -absorbing tissue. Fat is taken 

 from the lumen of the intestine with the greatest avidity by these cells. The judgment 

 in this case is based on the histological showing made by the epithelial folds after fat- 

 absorbing experiments. Unfortunately, no obser\'ations were made on the normal- 

 feeding salmon and no opportunity has arisen to repair the deficiency. The facts 

 presented here are wholly those derived from the studies of the young salmon which 

 had been fed fat by the methods described above. 



Figure 2, plate xii, from young salmon no. 45 presents a general view of the rela- 

 tions of the fat under a low magnification. Figure 3, plate xiii, is a highly magnified 

 drawing showing the fat of one of the loops of one of the mucous folds of the section shown 

 in figure 2. These figures show the epithelial cells gorged with fat for their whole extent 

 external to the mucosa. In some instances the fat drops are large and have a diameter 

 equal to or even greater than that of the normal cells. Often this fat appears in chains 

 of drops extending from the surface of the cell to the nucleus. In other instances the 

 droplets are somewhat smaller, but nevertheless crowd the cell body to the margin 

 These statements are made on the basis of observations in both the pyloric and the post- 

 pyloric loops of the intestine and on sections of the pyloric portion of the intestine. The 

 section from which figure 6 is drawn, representing the fat stained with osmic acid in a 

 fold of the coecal epithelium, also contains a section through the pyloric intestine. The 

 intestinal epithelium, too, is crowded with fat. In these epithelial cells the beaded 

 arrangement of fat droplets is especially prominent. Where the section is accurately 

 longitudinal through the epithelial cell, the rows of droplets of the larger size are shown 

 filling up the whole body of the cell and to extend from the free surface to the region of 

 the nucleus. It is comparatively seldom that fat is present in the basal portion of the 

 cells, i. e., within the nuclear zone, in any such massive quantity as is so often found in 

 the external limb of the cell. Here the fat is scattered along in fewer droplets, generalh 

 of fairly large size. In figure 5, plate xiii, the amount of fat in the inner nuclear zone 

 is comparatively small. 



It is to be emphasized that no fat droplets are present in the nuclei themselves. 

 We have not observed any nuclear fat either in the epithelial or in the connective tissue 

 nuclei supporting the epithelium of any portion of the alimentary canal. We are inclined 

 to think that the nucleus does not for some reason ever receive a deposit of fat. 



The intestinal epithelium discharges its fat into the connective tissue of the tunica 

 propria just as observed in the pyloric cceca. In the material from which figure 3 

 is drawn this fact is very patent. Here the tunica propria contains a comparatively 



