l6o BULLETIN OF THE BUREAU OF FISHERIES. 



any extensive mucous content of these young coeca. In the specimens that were fed 

 fat there was an occasional increase in the transparency, which was interpreted as due 

 to the presence of oil. In the intestine of such fish the excess of oil was easily and often 

 shown. 



EVIDENCES FROM SALMON FEEDING NORMALLY. 



Fat droplets were always observed in the epithelial lining cells of the pyloric coeca 

 of the Mont'^rey salmon. However, the fat was not present in all cells. Certain por- 

 tions of the epithelium were filled with fat droplets, while other portions were relatively 

 free. In almost every animal observed, and in different regions of the same animal, 

 certain extended portions of the epithelium were observed to contain no fat droplets, 

 while in the neighboring regions, often in the same section or perhaps in the next mucous 

 fold, fat would be present. These facts could not readily be explained by the assump- 

 tion that fat was loaded into these cells by way of storage, being brought in from other 

 portions of the body. On the other hand, such obser^^ations strongly suggest a process 

 of fat absorption. Previous observations on fat absorption in fishes are apparently 

 very limited ; at any rate the search in the literature has thus far revealed to the writer 

 only the observations of Van Herwerden ° "On Gastric Digestion in Fishes." This 

 splendid paper deals largely with digestion and the digestive enzymes. But it definitely 

 demonstrates fat absorption in Scyllium. It follows that the chief guide in the inter- 

 pretation of the present results is that to be found in the comparative literature on fat 

 absorption in other animals, a portion of which has been referred to and reviewed in a 

 previous chapter. 



The mucous epithelium of the salmon coeca is very extensive, considered in proportion 

 to the size of the tubes. The measurements of the superficial extent of the mucous coat 

 show that it is from 6 to 8 times the extent of the external surface of the coecum itself. 

 These folds are very complex in arrangement, though the epithelial coat itself is of uni- 

 form and simple type, a matter that is discussed in the paper presenting the normal 

 structure of these organs. It is this complex folding, and therefore the relative varia- 

 tion in the contact of the epithelium to portions of the contained food mass, that explains 

 the fact of unequal loading of fat in the epithelial cells. Hence there is no doubt that 

 the fat observed was absorption fat. 



HISTOLOGIC.'\L APPEAR.\NCE OF F.\T IN THE EPITHELI.-^L CELLS. 



A coecum containing fatty food material in an advanced stage of digestion and ab- 

 sorption will almost always present epithelial cells in all the stages of fat loading. The 

 appearance of the cells loaded with fat is characteristic and changes progressively as 

 absorption proceeds. In a general way, though some allowance must be made for the 

 comparison, the histological character of the cells would suggest three stages. 



Fat absorption, stage i. — The earliest stage of absorption is that of the passage of fat 

 into and through the superficial border of the epithelial cells. The methods of staining, 

 whether they be direct staining of the tissues with scarlet red or fixation and staining of 

 the fat by the osmic acid mixtures, show a large number of very fine granules in the 

 most superficial laver of the protoplasm of the cell. These fat granules are extremely 



o Van Herwerden, M., op. cit. 



