STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 1 33 



fish from the Ilwaco station, specimens which represent the first stage in the changes fol- 

 lowing the beginning of the fast, this layer is notably large. The granule cell layer is much 

 thicker and more prominent than in the normal Monterey salmon tissue. I have 

 made computations that indicate an actual increase of the mass of this granular layer." 

 The greater apparent increase in mass may be explained on the ground that the nor- 

 mal volume of the granule cell layer is retained while the volume of the various other 

 structures of the alimentary tract is sharply diminishing, a question that is now under 

 investigation. The structure of the cells in this layer does not materially change while 

 the other tissues around it are sharply degenerating. The cells remain loaded with 

 granules which have a strong affinity for the basic dyes. The loading of granules 

 remains characteristic of the cells even in the most degenerated salmon examined. 

 Here, again, one must interpret the granules as zymogen granules. Gulland ^ has given 

 the name eosinophile leucocytes to cells of this region, an identification to which I can 

 not subscribe. By implication he would ascribe to the granule cells a very different 

 function from that which appears to me to be the true one. The granules, which do stain 

 sharply with eosin as Gulland obser\'es, are too large to be compared with the granules 

 of eosinophiles. The granule cells themselves are larger, differently arranged, and have 

 a very different type of nucleus from the typical eosinophile. Also one never finds 

 granule cells of the type characteristic of the cells of this layer in the salmon blood 

 vessels of either the caeca or of the intestine. The matter is more fully discussed in 

 another paper, but the points are mentioned here in order to meet objections to the 

 view which is offered for the function of these cells; namely, the granule cell layer of 

 the pyloric caeca and of the alimentary tract of the salmon is an internal secreting organ 

 which has for its probable function the production of lipase. 



In the normal organ, when active digestion is going on, the lipase produced within 

 the granule cells is thrown out into the tissue spaces. Some of this lipase quite probably 

 reaches the epithelial layer and supplements the lipase produced by the epithelial cells. 

 Such lipase will, of course, facilitate the absorption and the resynthesis of the fats in 

 the epithelial cells, according to the laws of fat absorption. A considerable portion of 

 this layer lies outside the stratum compactum. It seems to me improbable that the 

 internal secretion of those cells will diffuse through the stratum compactum with the 

 same facility that it will pass out into the tissue spaces of the adjacent muscle coats. 

 The granule cell layer itself is almost free of blood vessels. The muscle coats, on the 

 other hand, are richly supplied with blood vessels. It would follow that any secretion 

 diffusing into the muscle coat would quickly be taken up by the blood, and would be 

 carried throughout the body. During the fasting period this lipase-producing function 

 of the granule cell layer is no longer of use in the absorption of fats but is of great sup- 

 plementary aid to the pancreas in maintaining an adequate suppl}' of lipase in the 

 blood. This offers an explanation that would account for the persistence of the organ. 



Increase in lipase from change in isotonicity of the tissues. — In the recent brilliant work 

 of the Rockefeller Institute in isolating and growing tissues of pure culture, it has been 

 shown that physiological activity, as measured by growth, is influenced by the degree 

 of concentration of the nutritive fluids. Tissues growing in physiological solutions of 



o These determinations were made by computing the cross-sectional area of the granule cell layer of cgeca from Monterey and 

 from Ilwaco salmon. The Ilwaco specimens exceed the Monterey by an average of 1 1 per cent. But the probable error is high. 



b Paton, Noel: Life history of the salmon. Article 3. The minute structure of the digestive tract of the salmon, and the 

 changes which occur in it in fresh water, p. 13, 1898. 



