l66 BULLETIN OF THE BUREAU OF FISHERIES. 



heavy loading of fat. Considering the whole of figure 2, the showing of fat in the 

 loop chosen for figure 3, plate xiii, is if anything too low for the tunica propria. In the 

 intestine also the fat that makes its appearance in the tunica propria is not distributed 

 over the whole of that structure down to the stratum compactum. The stratum com- 

 pactum forms a very definite and limiting boundary to the fat-containing tissue. 

 However, it is beUeved that this fat present in the tunica propria is not a true storage 

 fat. No characteristic areolar fat cells are present such as are found in such num- 

 bers in the pancreas and in certain other definitely adipose tissues of the salmon. 

 The tunica propria fat of the intestine is in comparatively small drops, rather evenly 

 distributed over the structure, and bears all the histological evidences characteristic of 

 the fat in the epithelial cells which is so obviously transient in its character. The fat 

 in the tunica propria of the intestine is also retained with greater persistencp, or at least 

 for a longer time folloOTng periods of fat absorption, than is the fat of the epithelial 

 cells. This characteristic has already been mentioned in discussing the ccEca. 



Further studies ought to be made before advancing the point, yet one must mention 

 here that no obvious lymph channels through which the fat is being removed have been 

 obser\^ed. That is, no structures comparable to the mammalian lymphatic radicles of 

 the mammalian intestine have been obser\-ed during these studies. This is not to be 

 interpreted as an assumption that there are none, because the observ^ations are insuffi- 

 cient in number to establish a point of this character. The fact must also be mentioned 

 that no evidence of accumulation of stainable fat in the cavities of the blood vessels has 

 been secured. In fact, fat droplets do not appear in any of the coagulated plasma nor 

 in any of the free blood cells in so far as yet observed either in the intestinal blood vessels 

 or those of other parts of the body. 



Minute liposomes have been found in the endothelial linings of blood vessels and in 

 the blood vessel walls. Such findings are shown in figures 3 and 6, plate xm. The 

 quantity of fat disposed in such places is small, but it was found to be present in fishes 

 in which fat absorption was at its maximum, a fact that suggests but does not prove 

 a relation to fat absorption. 



ABSORPTION OF FAT BY THE SALMON STOMACH. 



The fact of the absorption of fat by the epithelial lining of the stomach was first 

 observed on the young salmon which had been experimentally fed with fat. Obser- 

 vations were not made on the adult feeding salmon in a way to determine whether or 

 not gastric fat absorption occurred. The absorption of fat in the young was observed 

 in both series, i. e., the specimens from Brookdale, Cal., and from the McCloud River 

 at Baird, Cal. The young salmon in the McCloud River are feeding, but evidently on 

 a source of food which is not particularly rich in fats. At any rate the specimens 

 seined directly from the river and examined without further feeding showed onlv small 

 amounts of fat in the epithelium of the stomach. In the series of four young fish no 

 fat could be identified in one, a trace of fat only in one, and two contained obvious 

 and easily identified fat droplets. These specimens were taken as typical of the average 

 of those secured from the McCloud River, and were therefore considered as normals. 

 The specimens that received fat as food by the method previously presented were 

 examined in comparison with the normal series just given. 



