1 62 BULLETIN OF THE BUREAU OF FISHERIES. 



EVIDENCES IN ARTIFICIALLY FED SALMON. 



A brief report on these experiments has been presented. " The first series of experi- 

 ments carried on by the method of fat feeding described on the preceding page contains 

 two young salmon, one 14 and the other 16 centimeters long. 



Figures 6 and 7 present the histological picture of the amount of fat in the superficial 

 epithelium of frozen sections of the cceca from salmon 45. Absorption proved to be 

 extremely rapid and vigorous in this young salmon, not only in the coeca, but in the 

 intestine, as will appear later. The epithelial cells, especially of those mucous folds 

 which extended out into the lumen, were simply gorged with fat. The fat droplets were 

 extremely large and filled not only the superficial portion of the cells but the basal 

 portion as well. If the adjacent membranes of a deep fold were in contact with each 

 other, thus preventing a free contact with the fat of the coccal content, such places 

 would show a relatively small amount of absorption fat in the cells. On the free loops 

 of the mucous folds this situation did not exist, hence these portions were gorged with 

 fat in all the sections examined. This fact is shown especially well in the high magnifi- 

 cation of figure II. In some portions of the tissue in the neighborhood of the areas 

 drawn in this figure the fat was present in so great a quantity as to burst the cell mem- 

 brane. It was believed at the time of the preparation that the fat absorption con- 

 tinued until the quantity within the cells produced a pressure greater than the cell 

 surface could stand, hence the break, though one can not exclude the possibility of 

 mechanical pressure during manipulation. Drops often reach a diameter of from 8 to 

 10 /(, or even more in the young, which is greater than the normal diameter of the 

 epithelial cell, even at its largest end. 



In figure 6, showing the fat in salmon No. 45 stained with osmic acid, a number of 

 cells are shown in which the fat droplets of the outer portion of the cell are large enough 

 to take up the entire diameter of the cell. In different regions of this particular histo- 

 logical preparation other than shown in the figure there are numerous confirmations of 

 the above statement. 



Both the positive staining and fixation of fat by osmic acid and the arrangement 

 of fat vacuoles in corrosive fixed and paraffin sectioned material give confirmation of 

 the direct observations of the fresh material stained with scarlet red. The series oj studies 

 show thai fat absorption takes place abundantly in the pyloric coeca. Whatever else these 

 organs accomplish, it is perfectly clear that the absorption of fat is one of their chief 

 functions. 



FAT IN THE TUNICA PROPRIA OF FAT-FED SALMON. 



One of the most interesting confirmatory lines of observation which is largely 

 cleared up by the fat-feeding experiments is the fact of the presence of fat in the tunica 

 propria. In fasting salmon, especially in those used for control in the Baird series, 

 practically no fat is present in the tunica propria. One must be guarded in such state- 

 ments because this tissue holds on to its fat with great persistence. Fat will persist 

 in the tunica propria when one can demonstrate absolutely no fat in the epithelial cells. 

 But when absorption begins, as judged by the amount of fat in the epithelial cells, then 



o Greene, Charles W.: The absorption of fats by the alimentary tract, with special reference to the function of the pyloric 

 coeca in the king salmon, Oncorhynclnts tstha-^^ylscha. Transactions of the American Fisheries Society, 1911, p. z6i. 



