124 BUCLETIN OF THE BUREAU OF FISHERIES. 



lular fat, both when the muscles are small and immature and when they are larger, also 

 at a time when they are undergoing longitudinal cleavage. 



I have several stages of relatively young fish, from 7 to i6 cm. long, all of which 

 show a rich deposit of fat in the fibers of the superficialis lateralis. In the older fish," 

 as measured by the standard of size, there is a heavy loading of fat in the dark muscle 

 with corresponding separation of the bundles of fibrillae. There is, however, no disap- 

 pearance of fibrillae or other unusual characteristic than the distortion that comes from 

 the presence o'f such enormous quantities of fat. These remarks all apply, of course, 

 to the dark type of muscle. In the pink muscle there is little or no intracellular fat in 

 the muscle fibers during any phase of the growth cycle. This fat appears only after the 

 feeding ceases. 



It seems obvious that intracellular fat of the muscle can not, in the salmon, be 

 attributed to "fatty degeneration" in any true sense as signifying a protein degenera- 

 tion, or, for that matter, a protein cleavage. The amount of protein present does not 

 justify such a conclusion. 



MECHANISM OF F.\T TRANSFERENCE IN THE SALMO.N BODY. 



Fat metabolism in most animals, in the Mammalia for example, always involves 

 the two intertwined problems of most nutrition experiments, namely, fat intake and fat 

 mobilization. The former carries with it the detail of fat digestion, absorption, and the 

 laying down of the fats in the fat-storing tissues. The latter involves the taking up of 

 the fats from the storage tissues and their utilization in the production of new tissue or 

 in the liberation of energy, as the case may be, and such transferences in the body as 

 either method of utilization may entail. In most animals complete separation of these 

 two groups of processes involves more or less abnormal conditions for the animal. But 

 for the salmon the long fasting period is a perfectly normal process. We, therefore, can 

 make observations under the grim assurance that the salmon will not, in fact, can not, 

 eat. There is no added fat being absorbed during this fasting period, hence we have 

 present at this period only the uncomplicated mobilization and utilization processes. 



The discovery of a fat-splitting enzyme, or lipase, was made by Claude Bernard in 

 1846, and it was early suggested that the fats of absorption might be resynthesized in 

 the intestinal epithelium. It was not, however, until 1900, when Kastle and Loeven- 

 hart '' announced their brilliant discovery of the reversible action of lipase, that we 

 have had an adequate and thorough comprehension of the mechanism whereby the 

 animal body can transport fats from tissue to tissue. In light of the reversibility of 

 lipase action it is easy to see how a fatty infiltration can make its appearance in a tissue 

 so stable in structure as striated muscle, without assuming a disintegration of its pro- 

 toplasm, as in the fatty degeneration theories. 



In the problem before us I have already discussed at length the comparison with 

 regard to the actual loading of fat in the two chief types of tissue, the lateral dark muscle 

 and the lateral pink muscle. These are very difi'erent types of muscle, and, while the 

 problem and the controHing factors are essentially similar, it will greatly simplify the 



o I have during a number of years found salmon of various sizes entering tlie fresh waters, all of them e.Khibiting a great 

 variation in maturity of sex organs. These two facts, i. e., size and maturity, are independent of each other. 

 t" Kastle and Loevenhart: American Chemical Journal, vol. xxrv, p. 491 , 1900. 



