18 Investigations on the Life-History 



.food found in the intestinal tract. In the intestine of the trout 

 examined the remains of food were constantly present, and appeared to 

 consist mainly of parts of the exoskeleton and appendages of small 

 insects and crustaceans. In one case similar material was found in the 

 pyloric appendages, in other cases these were either empty or merely 

 contained eiitozoa. 



On microscopic examination of the appendages and intestine of the 

 salmon it is found that the pus-like material is due to a des- 

 quamative catarrh exactly like that found in the stomach (Fig. 6). 

 The mass in the tube is made up mainly of rounded cells staining 

 deeply with eosin, and having their nucleus rounded, somewhat varying 

 in size, but always staining deeply and uniformly with haematoxylin. 

 No chromatin network can be made out. In addition a few leucocytes 

 may be present and one or two shrunken goblet cells. The main mass 

 of cells is certainly derived from the degeneration of the columnar 

 epithelium, which in these cases is shed almost entirely from the folds 

 of the mucous membrane. It is almost always easy to find some spot 

 between the folds where this epithelium remains unaltered, and within 

 quite a short distance one can trace every stage of degeneration until 

 the same form as that lying free in the lumen is reached. Fig. 13 

 will make this clearer than any description. 



Sometimes the debris in the tube is more granular and the cellular 

 structure less easily made out, but that is evidently merely a later 

 stage of the same process. 



I have never found a salmon in the intestine and pyloric appen- 

 dages of which (for the two are always at the same stage of the process, 

 another proof of their identity of function) this change was not present 

 to a greater or less extent. The pyloric appendages and intestine of 

 the seven Berwick salmon were examined, and as these had all been 

 fixed immediately after death with sublimate, there could be no 

 question of post-mortem change. In four out of the seven the change 

 was practically complete, either the entire epithelium was degenerated, 

 or only a little was left deep down between the folds. In the remaining 

 three the change, though present, was less marked, being confined 

 mainly to the apices of the folds; in one there was very little catarrhal 

 change. In all the fish from the higher reaches, from the sea, and in 

 the kelts from the river the change was complete. It is very curious 

 to see the connective tissue framework of the folds, with its blood 

 vessels much congested as a rule, lying absolutely bare of epithelium in 

 this pus-like mass (Fig. 6). 



This change must certainly be a pathological, catarrhal, or seasonal 

 one, for in the trout we see nothing of it. There the columnar 

 epithelium everywhere covers the folds, both in the specimens fixed 

 immediately after death, and in those fixed at varying times post- 

 mortem, except in the intestine of the specimen fixed six hours after 

 death. Here there is indeed a considerable desquamation of 

 epithelium, which is lying free in the lumen of the gut, but the cells 

 are not degenerated in any way. They still exhibit the characteristic 

 hem, their nuclei show the chromatin network, and the desquamation is 

 probably accidental, and due to some squeezing of the specimen before 

 it was fixed. 



There is one source of fallacy in these cases, or rather what might be 

 regarded as a source of fallacy, that is the presence of parasitic worms 

 in the intestine and pyloric appendages of the salmon. There are few 

 fish which are entirely free from these, and sometimes the intestine is 

 greatly distended with them. It might be thought that these were the 

 cause of the catarrh, and indeed one finds on section that in some of 



