172 BULLETIN OK THE BUREAU OF FISHERIES. 



In fact, Weiss states that in the young cat the stomach has the power to absorb fat, 

 but this power is lost after a few months. Experiments carried out in this laboratory" 

 indicate that the ordinary laboratory mammals — the rat, the cat, and the dog — possess 

 the power to absorb fats not only in the young but in the adult. 



It would seem, therefore, that the process of fat absorption in the stomach does 

 take place with somewhat greater ease and facility in the young than in adults, but 

 we are convinced that it is a function of the stomach which is retained throughout life 

 and not lost at an early stage of development, as claimed by Weiss. 



The process by which fats are taken up by the mucosa of the alimentary canal is 

 quite naturally brought in question. The histological method used here does not follow 

 the digestive processes. But there are certain facts under constant observation which 

 indicate the nature of the absorptive process. The introductory quotation from Wells 

 sets forth in terse and concise terms our current views of the mechanism by which fats 

 are absorbed. Not only that, these views apply to the mechanism of fat transference in 

 the body in general. Our general conception is that lipases are produced in the body 

 and that through a process of dissociation the fats are split into easily diffusible forms. 

 This dissociation takes place in digestion. In the resulting diffusible form the fats can 

 readily enter the superficial border of the epithelial coat. The laws of lipolysis, as 

 formulated by Kastle and Loewenhart,* readily account for the resynthesis of fats when 

 once the fat cleavage products are present and in sufficient concentration within the 

 walls of the cells. That this is the process in the salmon is indicated by two proven 

 facts — first, the fact that fat droplets are never found exactly in the striated borders of 

 the superficial epithelial cells of any portion of the alimentary tract of the salmon; the 

 second fact is that these cells in the height of absorption are loaded with fat droplets of 

 such size and numbers as to gorge the bodies of the cells. In fact, numerous histological 

 pictures indicate that the cell boundaries are under internal tension or pressure. Figure 

 1 1 , plate XV, as also a number of the other figures presented here, gives one a conception 

 of the physical condition of the cell when loaded with fat. This condition can be 

 explained by two links in the chain of evidence assumed by our present theories of 

 fat mobilization. The first of these is the fact that during rapid digestion of fats, say 

 in the cavity of a pyloric coecum, the fatty acids and the glycerin will diffuse through 

 the free wall of the columnar epithelial cells at a very rapid rate. Synthesis within 

 the cell will convert these fat cleavage products into the relatively inert fat molecules 

 which accumulate in ever increasing quantities. This removal of the cleavage products 

 maintains an osmotic condition favorable for further and continued diffusion into the 

 cell, thus producing a distinct pressure in an already mechanically overdistended tissue. 



Emphasis can be laid on this process as an explanation of the enormous loading 

 of the fats, as shown especially in figures 4, 5, and 8; also in lesser degree in a majority 

 of the figures presented. In many instances the fat droplets within the cells are so large 

 as to occupy the full diameter of the cell, and so numerous as to load the entire outer 

 end of the cell from surface border to nucleus. When an epithelial cell is thus loaded 

 with fat the fat is of mechanical necessity arranged in the regular beaded rows that give 

 the diagrammatic appearance which is often presented by the figures. 



« Greene and Skaer, op. cit. 



t> Kastle and Loewenhart; Concemins lipase, the fat-splitting enzyme, and the reversibility of its action. American Chemical 

 Journal, vol. >;xiv, 1900, p. 491. 



