FAT-ABSORBING FUNCTION OF ALIMENTARY TRACT OF KING SALMON. 1 67 

 ABSORPTION AFTER FAT FEEDING. 



The amount of fat taken up by the mucous lining membrane of the stomach is not 

 anywhere near so great in amount as that shown by the mucosa of other portions of 

 the ahmentary tract in one and the same animal. However, this fat is in amount 

 quite sufficient to form a very striking picture. 



The microscopic evidence of fat absorption is largely limited to the superficial 

 epithelium. At any rate, this tissue is most distinctly loaded with fat droplets, and the 

 loading apparently occurs earlier than in deeper portions of the gastric mucosa. An 

 examination of the epithelium of the stomach showed fat droplets present in practically 

 every portion of that organ. The absorption takes place not only in the cardiac divi- 

 sion, but also in the pyloric stomach. 



The earliest indication of fat absorption is found in the appearance of fat droplets 

 in the more superficial epithelium and in the distal ends of the cells. As time is allowed 

 for the digestive and absorptive processes these cells become more fully loaded — in fact 

 gorged — with fat, first in the outer limbs, then later the droplets appear nearer the 

 bases of the cells. The glandular tissue of the gastric mucosa also shows the presence 

 of fat droplets in the later stages of fat absorption. Apparently not only the super- 

 ficial epithelium and the crypts even down to the neck cells, but also the glandular 

 cells themselves are capable of taking up fat in quantities sufficient to produce the 

 numerous droplets which the microscopic examination reveals. Since the structure 

 of the gastric mucosa is characteristic and strikingly different in the two divisions of 

 the salmon stomach, these regions \vill be discussed separately. 



ABSORPTION IN THE CARDIAC STOMACH. 



In the series of fish fed at Baird one had little or no fat in the stomach coat, while 

 three showed the presence of fat in decided quantities. In those fish in which fat was 

 present in the stomach it was in relatively large amounts as compared with the normals. 

 That is to say, the amount of fat in the epithelium of the stomach in the fat-fed fish 

 was larger in amount than in the fish coming directly from the river. 



The amount of fat in process of absorption by the epithelium was greatest in fat- 

 fed fishes nos. 88 and 91 of the McCloud River series. The fat was present in super- 

 ficial epithelial cells of both the cardiac and the pyloric divisions of the stomach, but 

 the amount in the cardiac division was very obviously less than in the pyloric division. 



The fat in the cardiac stomach is distributed chiefly in the cylindrical cells of the 

 superficial epithelium. It is in greatest quantity in those cells bordering freely on the 

 cavity of the stomach. In a typical section through the cardiac region all that portion of 

 the epithelium outside the nuclear zone and within the extreme outer clear zone will be 

 studded with minute fat droplets. The fat droplets here vary much in size, but seldom 

 reach more than 3 /z in diameter. The most of the fat is in such small divisions as to 

 require an oil immersion lens to distinguish the individual droplets. (See fig. 4, pi. 

 xin.) In the outer clear zone or border I found fat in only one fish, and in this instance 

 the droplets were extremely minute, i. e., liposomes. " 



a The size of the fat droplets in the stomach shows every gradation from the larger size of 2 to 3 /i diameter dov\-n to a size that 

 is disccmable only with the highest magnification. In the salmon stomach, indeed in the salmon tissues in general. I am quite 

 .unable to distinguish any constant differences in appearance among these fats. There is no line to be drawn either as regards 

 color, size, or contour. It is true that the color shade and the size vary greatly, but not in any way that does not admit of expla- 

 nation without assuming any characteristic difference in the composition of the fat bodies stained. Under these conditions I 

 use the term liposomes without reference to the kind of fat. only to designate the extremely small size of the droplets. 



