452 



probably accidental, and due to some squeezing of the specimen be- 

 fore it was fixed. 



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

 might be regarded at 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 the intestines which contain them there is nothing left 

 but the muscular coats and a mere shred of connective tissue infil- 

 trated with leucocytes. But they are almost as common in the trout 

 as in the salmon, and there their presence does not produce a des- 

 quamative catarrh, but simply a flattening out of the folds of the 

 mucous membrane from distension; the epithelium remains intact. It 

 is noticeable, however, that when these worms are present the number 

 of goblet-cells in the epithelium is always unusually large, sometimes, 

 indeed, the goblet-cells considerably exceed the ordinary epithelial cells 

 in number, as if the irritation caused by the presence of the worm 

 necessitated a greater flow of mucus to lubricate the surface of the 

 mucous membrane. 



The Pancreas. 

 This is not gathered into a compact organ, but the acini are 

 scattered more or less difi"usely through the long strands of intra- 

 peritoneal fat lying round the stomach, pyloric appendages, and in- 

 testine (Fig. 8). The microscopic ducts — one can hardly call them 

 interlobular or intralobular, as there are no true lobules — are lined 

 with a cylindrical epithehum, and resemble the ducts of mammalian 

 salivary glands much more than those of the mammalian pancreas. 

 The cells of the secreting acini are like pancreas-cells elsewhere, and 

 they evidently go through exactly the same cycle of appearance during 

 the formation and extrusion of zymogen granules as those descri- 

 bed by Langley. One point of difference there is, however, inasmuch 

 as in the trout and salmon the zymogen granules in the pancreas, as 

 in the stomach cells, stain a deep black with iron-haematoxylin, which 

 renders it very easy to make out the stage of secretion. Fig. 9 

 shows a pancreatic acinus where the cells are full of granules, the 

 so-called stage of "rest", when no extrusion of granules is going on, 

 but where they are being heaped up in the cell ready to aid the pro- 

 cess of digestion. Fig. 10 depicts an acinus where the granules have 

 mostly been extruded, the so-called "active" stage. The only pancreas 



