STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. 1 19 



liberating tissues. The tissues, in short, can utilize the energy of fats by direct oxida- 

 tions. It remains to examine the facts submitted and to discover, if possible, the 

 mechanism whereby this great store of salmon fat is rendered so labile and so wonder- 

 fully efficient in the execution of the activities of this last lap of the salmorj life cycle. 

 Of all the facts presented it seems to me the most significant are: 



I. The appearance of intramuscular fat in the pink mu^le at the beginning of the 

 spawning migration, and 



II. The maintaining of a relatively uniform distribution of this fat in the fibers 

 until the death of the animal. 



Just as soon as the salmon ceases to feed, and the products of digestion no longer 

 reach the active musculature, then, and not until then, there is thrown into the pink 

 muscle fibers a supply of fat adequate to the energy needs of this most critical period 

 in the salmon life cycle. The excess of fat is deposited in an extremely finely divided 

 state and is brought into intimate contact with the fibrillae, one can almost say with 

 the sarcous elements. Certainly in many rows of fat droplets between the fibrillae the 

 individual liposomes are in close approximation with corresponding sarcous elements in 

 the fibrils. One can not escape the inference that this microscopic emulsion of the fat, 

 its general distribution throughout the muscle fiber, and the intimate relation with the 

 elemental fibrillar structure, all point to an immediate utilization of the fats in the pro- 

 duction of muscular energy. 



This hypothesis is further supported by the observations on the cheek muscle and 

 on the fin muscles, all muscles in much more uniform, though less intense, activity than 

 the lateral muscle. These muscles carry a light but strikingly persistent load of minutely 

 di\'ided intramuscular fat during the entire migration. They never have a great excess 

 of storage fat, either intermuscular, as in the pink muscle, or intramuscular, as in the 

 dark muscle. 



The great fat storehouses are the intermuscular fat of the great lateral pink muscle, 

 the inter- and intra-muscular fat of the dark muscle, and the fat of theadipose connective 

 tissues. With the cessation of feeding no further fats, proteins, etc., are brought in as 

 foods. With the external food supply now shut off the physiological mechanism of the 

 salmon must turn to the food materials on hand, to the internal food supplies of the 

 salmon's own body. The internal supply is limited to body tissues as such, and to the 

 fats. It is the fats that are immediately drawn upon. From the fat deposits the fat is 

 gradually but regularly transported to the active muscles, where it is maintained in a 

 uniform and favorable distribution, and in amount adequate to supply the energy 

 expended by the salmon in the migration fight against the currents and rapids of the rivers 

 on its way to the spawning beds. 



TRANSPORTATION OF FATS IN THE FASTING SALMON. 



HISTORICAL. 



The histological observations on the king salmon have given every confirmation 

 of Miescher's original assumption, based on his study of the Rhine salmon, that the 

 fat of the salmon can be transported from one part of the body to another; i. e., from 

 tissue to tissue. He laid special emphasis on the utilization of the muscle fats in the 

 building up of the fats of the ovaries, but he also suggested that fat was the source of 



