FAT-ABSORBING FUNCTION OF ALIMENTARY TRACT OF KING SALMON. l6l 



small, ihe largest being less than i /i in diameter. In some instances they appear in 

 such minute size that they are only just distinguishable under the oil immersion. As 

 absorption proceeds the fat granules make their appearance deeper and deeper in the 

 cell, loading up the zone between the free surface and the nucleus. Here the fat droplets 

 are relativelj^ large, ofttimes being 4.5 to 6 u in diameter. In the intermediate area and 

 between the superficial zone and the extra-nuclear zone are all sizes of fat droplets from 

 the extremely minute ones just described to the large ones in the extra-nuclear zone. 

 This picture is shown very clearly in figures 6 and 12. 



Fat absorption, stogc 2. — The second characteristic cellular appearance, which is des- 

 ignated as stage 2, consists in the filling of the inner or basal end of the cell with fat 

 droplets. Not only that portion external to the nucleus will be loaded with fat, but 

 the portion between the nucleus and base of the cell will also contain an excess of fat 

 droplets. 



The sizes of the droplets in the end of the cell are similar to those just external to 

 the nucleus, but the number of droplets is rarely so great. When the cell is fully loaded 

 it generally happens that fat will be found in the connective tissue of the tunica propria 

 beneath. If fat absorption is continuous at this stage, as one might legitimately assume 

 from the histological appearance, it is obvious that as the fat is entering the outer zone 

 it will at the same time be discharging from the inner zone and passing into the chan- 

 nels which distribute fat through the body. Knoll "■ has recently reported experiments 

 on fat absorption in the mammalia in which this condition is shown to hold. 



Fat absorption, stage j. — When absorption from the lumen of the coecum ceases, the 

 outer margin of the cell begins to clear of fat. This disappearance of fat apparently 

 slowly and gradually extends over the whole area of the cell external to the nucleus. 

 In favorable material in this stage epithelial areas will be found in which the outer or 

 extra-nuclear zone of the mucous epithelium is almost, sometimes entirely, free of fat 

 droplets. Still, fat droplets will be present in considerable quantity in the inner or basal 

 zone. As a rule the basal portion of the cell will contain relatively large droplets in this 

 stage and the connective tissue supporting the cell will be similarly loaded with fat 

 droplets. However, some groups of cells are found in which the fat droplets in the 

 basal portion of the cell are extremely minute, as shown in figure 13. In this particular 

 figure the basal areas are heavily loaded with fat in extremely fine subdivision. The 

 adjacent connective tissue of the tunica propria contains a similar distribution and size 

 of fat droplets. 



These three stages of course are only phases of an orderly and progressive process 

 in which the fat enters the outer zone of the cell, is disposed within the substance of the 

 cell in droplets, and is ultimately distributed from the cell to the basal pole, the opposite 

 from which it entered. The variations in the size of the droplets in different zones of 

 the epithelial cells, especially the extremely small droplets in the outer portion of the 

 cells and the fine droplets in the bases of the cells at the time the discharging is almost 

 complete, are very interesting when considered in relation to the theories of fat absorp- 

 tion. But the discussion of these theoretical points will be taken up again in a later 

 section of the paper. 



a Knoll, A.: Chemische und mikrosopische Untersuchungen uber den Fetttransport durch die Darmwand bei der Resorp- 

 tion. Pfliiger's Arcbiv, bd. 136, 1910, p. 208-247. 



