STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 83 



Cohnheim's areas. In these locations very large drops, comparatively speaking, are 

 present. They are usually quite uniformly distributed over the surface of the fiber as seen 

 in a cross section. The intracellular droplets vary in diameter from 3 to 6 ;«. Beside the 

 larger droplets there are always numerous smaller ones of varying sizes down to a fraction 

 of a micron. Medium to small droplets may be present in close relation to the larger, 

 all more or less evenly distributed among the larger droplets. The smallest droplets 

 are of liposomic size and are deposited in shorter or longer chains between the fibrillEe or 

 groups of fibrillae. There is evidence that these liposomes" are arranged with reference to 

 the striations of the fibrillae, and it is suggested that such relation is of significance in 

 reference to the function of the fats in the muscle. 



Occasionally I have found an enormous fat drop filling up the whole central 

 portion of the dark muscle fiber, the protoplasm of the fiber forming a band-like ring 

 around the drop (fig. 14, pi. ix). Even in these cases the protoplasmic ring is closely 

 studded with smaller fat droplets, in one case as many as 19 droplets 2 to 4 // in diameter 

 being crowded within the circumference of this protoplasmic ring. 



The superficial lateral muscle begins receiving its excess of fat early in the develop- 

 ment of the fish, at least as early as the fingerling stage. In this respect the muscle is in 

 marked contrast to the deep lateral muscle, in which there is little or no deposit of inter- 

 muscular fat until a considerably later stage in the development of the salmon and no 

 intramuscular fat until maturity. 



The main points which characterize the fat disposal in the normal adult trunk 

 muscles may be summarized as follows: 



Summary of fat disposal in the normal muscular tissues. — i. The fat is most heavily 

 Stored in the superficial lateral muscle, where it is present in enormous quantity both 

 between the muscle fibers and within the fibers. This tissue is heavily loaded with fat 

 at a very early stage, at least by the 7-centimeter stage, and is always found loaded in 

 the feeding fish. 



2. The great pink muscle contains little or no fat between the fibers in the fingerling 

 stage, but it has a small amount of such fat in the small Monterey Bay fish. The amount 

 of this intercellular fat increases to its maximum at the time when feeding ceases. The 

 intermuscular fat observed at Ilwaco is relatively high. While it is probably less than 

 at the time of cessation of feeding, it is certainly more than at Monterey Bay. 



3. There is no intracellular fat in the pink muscle during the feeding stage, or, at 

 most, a trace of liposomes in the smallest pink fibers. The liposomic fat makes its 

 appearance after the fast begins. An exception is found in the superficial zone next the 

 dark muscle. 



4. The fat in the fin and the head muscles is relatively insignificant in amount. 

 It is both inter- and intracellular in its relations to the muscle fibers. 



a Various terms have been used to designate the microscopic fat droplets or fat-like droplets. They were first described by 

 Kolliker as interstitial granules. This was before their fatty nature was sufficiently well known. In fact. KoUiker thought they 

 were not true fat droplets. The term liposome was introduced by Albrecht to describe those interstitial granules of muscle which 

 are demonstrated by the scarlet red stain. Bell has used the term " interstitial granules. " but he considers the granules that take 

 the scarlet red stain as used in his paper as fat bodies to which the term "liposomes" is applicable. (For historical discussion of 

 the subject see Belt, Internationale Monatsschrift fiir Anatomic und Physiologic, bd. xxvm, p. 297; also Anatomical Record, vol. 

 4, p. 199.) The term liposome is used in the present report to indicate the microscopic fatty bodies staining with scarlet red and 

 of small size, usually under 3 it, that take the characteristic scarlet red stain. It is not intended to carry any meaning suggestive 

 of the chemical character as regards the specific kind of fat, though it is the opinion of the writer that neutral fats are the ones 

 dealt with in the salmon tissue described in this paper. 



