FAT-ABSORBING FUNCTION OF ALIMENTARY TRACT OF KING SALMON. 1 63 



fat begins to appear in the tunica propria in an increased quantity. After 18 hours or 

 more (see figs. 6, 7, and 8), the connective tissue layer supporting the epithelial cells 

 becomes extremely full of fat droplets. The fat appears first in the vicinity of the 

 bases of the epithelial cells, then is distributed through the substance of the tunica 

 propria. The stratum compactum alwaj-s forms a definite and striking boundary to 

 the fat containing tissue of the tunica propria. This is shown especially well in the 

 figures, particularly figure 6. 



The tunica propria acts as a sort of reservoir for the fat immediately following 

 periods of active absorption. The matter has not been sufl[iciently studied yet, but it 

 seems obvious that the tissue building up this stratum of the coecal wall seizes and holds 

 fat with unexpected persistence. Fat will be found here in a relatively considerable 

 number of droplets at a time when the epithelial cells are completely discharged. 



The stratum compactum, as described in the discussion of the normal structure, 

 forms a continuous sheath around the tunica propria. It is a continuous membrane 

 with no discernible openings other than at the points where blood vessels enter. Any 

 fat passing through the stratum compactum would have to pass through in solution or 

 else be carried within in the lumen of the blood vessel. In either case no definite fat 

 globules as such get by this membrane from the tunica propria. 



PROTOCOLS. 

 Brookdale Salmon, Field Series No. 45, Length 14 Centi.meters, Take.n July 6, 1911. 



This young salmon was a 2-year-old reared by the Brookdale hatchery, California. It was taken 

 from an aquarium and transported to the Hopkins Seaside Laboratory, Pacific Grove, Cal. This 

 salmon was fed fat. In this instance it received first a fat emulsion consisting of 20 per cent olive oil 

 in coagulated milk injected into the stomach through the mouth. This feeding did not seem to be 

 very successful and was followed later by an injection of olive oil into the rectum. This method of 

 feeding proved to be very successful, convenient, and satisfactory. The salmon was killed after allow- 

 ing 18 hours for absorption of the olive oil (22 hours, counting time from the first attempt to feed by 

 way of the mouth). Frozen sections were made of the fresh tissues, and certain portions of the tissues 

 were fixed by different histological methods for later examination. 



Fat in the pyloric cceca. — The epithelial cells are simply gorged with fat droplets. Especially are 

 the outer ends of the cells so filled that the cell boundaries are obscured. The diameter of the droplets 

 varies widely. The larger drops distort the cells. The basal ends of the cells contain a much smaller 

 amount of fat. 



The tunica propria is also well filled with fat, but not so great an amount as in fish 46. The drops 

 are more uniform in size. This fat extends deep into the folds of the stratum compactum, but is never 

 present in its substance. 



Fat in the intestine. — The epithelial cells are as much crowded with fat as in the coeca, as shouTi 

 in figures 2 and 4. The deeper folds of the intestinal mucosa are not always filled with fat, at 

 any rate the amount of fat is not nearly so great as in the outer folds. 



There is less fat in the intestinal tunica propria than in the caeca of the same animal. 



Brookdale Salmon, Field Series No. 46, Length 16 Centimeters, Taken Jlt.v 6, 1911. 



This young salmon was a mate to no. 45 and was transported at the same time. It was fed fat 

 by rectal injection only, and was killed after 42 hours of absorption. Frozen sections were prepared 

 and tissues were also fixed for permanent histological mounts. 



Fat in the pyloric caeca. — The amount of fat in the epithelium of the pyloric ccEca varied in different 

 preparations. Those cells on the tips of the folds were crowded with fat, while those in the grooves 

 between folds were relatively free. Figure 8 and figure 11 are from this specimen. 



The tunica propria, as shown in figure 8, was more crowded with fat than in no. 45. 



