Greene. — Absorption of Fats in Salmon 269 



Dr. Ward : Have you tried this on fish after they leave salt water, 

 so that you can say whether there is any absorption? 



Dr. Greene : That question I suspect does not mean as much to 

 some of the gentlemen present as it does to the gentleman who asked 

 the question. Those who are familiar with the situation know that the 

 king salmon do not eat after they leave salt water on their return 

 journey to the fresh waters for spawning purposes. A still larger 

 number do not know that in this fasting journey there is a marked 

 retrogression in the whole alimentary tract. That is a problem I have 

 been working on and I now have a considerable mass of scientific ma- 

 terial tending to show that this tract not only markedly degenerates 

 in size, but changes in a very profound way in histological structure. 

 These changes in structure practically answer the question. 



One would not expect the salmon that have undergone the extreme 

 changes to show the same absorbing power that the young salmon 

 do that were eating but had not yet gone to sea; or that the old salmon 

 still eating and in the sea show. The fact is that the epithelial coat of 

 the cceca has practically disappeared. I have histological sections of 

 material of far-changed spawning salmon in which there is no epithe- 

 lial coat present either on the cceca or on the intestine. So, of course, 

 in such cases absorption would be wholly different from the normal 

 absorption of food material. 



Dr. Ward : Taking them about the time they stop feeding, can you 

 keep them absorbing longer than they otherwise would? In other 

 words, does the stoppage of absorption follow the stoppage of feeding; 

 or does the stoppage of feeding become associated with the tendency 

 to degenerate in the alimentary canal? Which is the primary and 

 which is the secondary feature? 



Dr. Greene : I have not made those tests and do not think I can 

 answer the question. It is a factor that is too much involved in cer- 

 tain physiological processes to be directly determined by histological 

 evidence alone. It is also very difficult to detect the moment when 

 the normal structure begins to change over to this special degenerative 

 structure. I suppose that in the earliest stages of this change the 

 tissue, having already entered a pathological state, may still be capable 

 of absorbing, though I doubt it. I do not know ; I am only guessing 

 at that. I cannot guess with assurance in our present state of 

 knowledge. 



The interesting factor behind these questions asked by Dr. Ward is 

 this factor of degenerative change, not only in the alimentary tract but 

 in all other parts of the body save one, the reproductive organs, 

 during the migration from the feeding grounds of the sea back to the 

 spawning grounds. This is one of the most interesting of biological 

 facts, as far as its physiological bearing is concerned. I am personally 

 of the opinion that the cessation of feeding, therefore of absorption, 

 and the broad changes in the skin, muscles, etc., are all expressions of 

 the one physiological condition that culminates in the spawning process. 



