STORAGE OF FAT IN MUSCITlaR TISSUE OF KING SALMON. 1 29 



the tniiik pink muscle. The deposit of liposomes in the intermediate zone of pink 

 muscle fibers is occasioned by this greater concentration of lioase. 



If it can be granted that the dark muscle retains this assumed power of lipase 

 production throughout its whole life, then it will follow that at the spawning grounds 

 we wll still have in this particular tissue more than the average amount of lipase in the 

 muscle fluids. If so, there wall be a tendency to hold fats and fatty acid in solution 

 in this tissue, and, other things being equal, the tendency to maintain a somewhat 

 higher content of fat in the form of liposomes. 



The liposomes will form in those tissue spaces in which there is greater stagnation 

 of the tissue fluids. In so far as the dark muscle is concerned, this point is immediately 

 under the sarcolemma. Should the cleavage products of fatt}' acid and glycerin 

 diffuse from the sarcoplasm through the sarcolemma, then it would be picked up ulti- 

 mately by the blood stream and washed away. If, on the other hand, fats are coming 

 into the pink muscle, then the diffusion will pass first through the sarcolemma and then 

 the sarcoplasm, which is using fat in its oxidations. Therefore, the central portion of 

 the muscle fiber will contain fewer liposomes and smaller ones while the superficial 

 portion and the region immediately under the sarcolemma will contain relatively larger 

 liposomes. This picture corresponds to the facts whether or not the theory offered in 

 e.xplanation be true. The factors discussed in previous pages which determine the number 

 and size of the liposomes are therefore the same for dark muscle as for the pink, except 

 for one, namely, the factor b, given on' page 126, the relative abundance of lipase in the 

 dark muscle. This factor b is greater than in the pink muscle, since the dark muscle 

 itself is presumed to be producing lipase. 



RELATIVE ABUNDANCE OF STORED FAT AND ITS DISPOSAL IN THE ORGANS. 



Jly chemical analyses have shown that there is always a great variation in the per- 

 centage of fat taken from any standard region of different individual salmon from any 

 particular station. No school of salmon contains individuals of uniform characteristics 

 as regards either size or condition, for example, the specific loading of fat. Considering 

 onh' the region under discussion here, namely, the mid-lateral portion of the body, I 

 find that there is great variation in the total amount of fat present. In the histological 

 examination of the variation of fats this will show itself in the number and especially in 

 the relative size of the fat droplets. The loading of fat, as indicated by these facts, is 

 most constant in the salmon obtained at the mouth of the Columbia River. It is to be 

 assumed that if one could obtain salmon just in the region where and at the time when 

 they cease feeding, then the loading of fat would be most nearly constant. Even then 

 a great variation might be expected, since in salmon of the same size it can not be 

 assumed that there has been uniformity of opportunity in obtaining food during the 

 long period of development. Therefore, there are great variations present in the total 

 loading of fat in the lateral pink muscle, even at the Ilwaco station, variations that are 

 the expression of a multiplicity of factors. 



As salmon pass up the rivers in their migration and since the stored fat forms the 

 total source of the energy-giving material, it follows that there will be a diminution in 

 the total fat directly proportional to the length of time and the relative expenditure of 

 energy since the beginning of the fast. 



Instances of variations in fat between the fibers of the lateral pink muscle at the 

 first station, Ilwaco, are to be obtained by reference to the protocols of fishes nos. 11 1, 



