134 BULLETIN OF THE BUREAU OF FISHERIES. 



slightly lower tonicity than that to which the tissues are adapted, undergo a more 

 active growth than those in fluids of relatively high tonicity. .These factors have been 

 worked out on several tissues, but very strikingly on the rate of healing of wounds in the 

 skin of frogs which had their body fluids decreased in tonicity by injections of water." 



I have no doubt that these principles are operative in the salmon during the migration. 

 The salmon tissues in this stage of the life cycle are most of them long past the period 

 where growth is the prominent physiological activity. There is, however, one marked 

 exception, namely, the reproductive organs. These organs are quite immature at the 

 time the migration begins. They suddenly take on an active stage of growth which 

 proceeds readily till complete development at the time of spawning. Other tissues 

 show their variations in physiological activity in ways other than growth, the muscular 

 tissues in increased production of energy, the glandular tissues by variation in secre- 

 tory activity, etc. 



In work on the Sacramento River '' I showed that there is a marked decrease in 

 the depression of the freezing point of salmon serum as the fish migrate from the sea to 

 fresh water. The depression of the freezing point is a direct measure of the tonicity of 

 the blood. As this diminution begins with the process of migration from salt water to 

 fresh water it is evident that it will have the same type of influence on the tissue 

 activities of the salmon as that shown in the experiments on tissue growth. This is 

 undoubtedly a factor in the stimulation of the reproductive organs to the sudden 

 increased growth which takes place in the salmon at this time. It is a safe inference 

 that this change in isotonicity of the blood and tissue fluids if exerted on other 

 tissues of the bodies will cause variation in their physiological activity. Applying this 

 principle to the pancreas and to other tissues where lipase is produced we have a factor 

 accounting for an increase in metabolites, of which Upase is one, at the critical time of 

 the beginning of the migration. 



Lipase jrom tissue degenerations . — Another source of lipase may arise through tissue 

 degenerations. Extensive degenerations are taking place in the alimentary tract. 

 At Ilwaco the mucous membrane of the intestine and pyloric caeca has already reached 

 a considerable degree of disintegration. On the current theories explaining degenerative 

 change one may assume that these cells have already passed through a stage of physio- 

 logical hypertrophy. Kastle and Loevenhart have shown that these cells are active 

 lipase producers in the normal condition. Therefore, one may assume that the inflam- 

 matory condition preliminary to the actual necrosis is associated with an increase in 

 lipase production. The disintegration of the cells and especially the chromatolysis is 

 the final step in the process. These pathological changes accelerate the physiological 

 production of lipase in the mucous epithelium of especially the pyloric caeca just at the 

 time when such an increase in lipase is of most value to the salmon, namely, at the 

 beginning of the fast. Lipase from this source would almost cease at a quite early stage. 

 However, the epithelium is rarely wholly disintegrated. 



Lipase from the liver and other tissues. — There is evidence that other tissues of the 

 salmon are more important in producing Upase. Of these one may mention the liver, 

 whose function in this regard will be presented in another paper. 



o Ruth, E. S.: The influence of distilled water ou the healing of skin wounds in the frog. Journal of Experimental Medicine, 

 vol. 13, p. 422. I9II. 



ti Greene, C. W.: Physiological studies of the Chinook salmon. Bulletin U. S. Bureau of Fisheries, vol. xxiv, 1904, pp. 446,449. 



