of the Salmon in Fresh Water. 23 



4. CHANGES IN THE DIGESTIVE ACTIVITY OF THE 

 SECRETIONS OF THE ALIMENTARY CANAL OF 

 THE SALMON IN DIFFERENT CONDITIONS. 



BY A. LOCKHART GTLLESPIE, M.D., F.R.C.P.E., F.R.S.E. 



1. PRELIMINARY. 



As already pointed out, the question of whether salmon feed during 

 their sojourn in the river has been much debated. The absence of food 

 from the alimentary canal has been variously explained by activity of 

 digestion or by the power of rejecting the contents of the stomach when 

 the fish is captured. 



Dr. Gulland's investigations have demonstrated the occurrence of a 

 degeneration of the mucous membrane of the alimentary tract during 

 the stay of the fish in the river, and very clearly indicate that little or 

 no absorption of food can go on. 



In this investigation the digestive activity of the various parts of the 

 alimentary tract is considered. 



The points investigated are the proteolytic and diastatic powers of 

 extracts made from the mucous membrane lining the stomach, the bowel, 

 and the pyloric appendages, and the variations in these in relation to 

 the season and the part of the river from which the fish were obtained. 



It is well known that the peptic digestion of proteids in cold-blooded 

 animals owes its activity at low temperatures it can take place at C. 

 to the large proportion of pepsine present in the secretion of the 

 gastric glands. 



There are two considerations concerning the degree of activity of 

 enzymes, or unformed ferments, which apply to the subject under dis- 

 cussion. The first is that the amount of digestive action exerted by any 

 agent is in direct proportion to the quantity of enzyme present, while 

 the second is that enzymes are more active in media as the temperature 

 rises from deg. to 40 degs. Cent., their power gradually diminishing 

 as the temperature rises above 40 degs., until at 70 clegs, all activity 

 ceases. 



In fish the large proportion of pepsine .allows rapid proteolysis to take 

 place in the stomach, although the temperature at which it occurs may 

 be low, and if the active secretion be tested outside the body at a higher 

 temperature, a very much more powerful action is exerted on proteids 

 than by the ordinary peptic extract obtained from the gastric mucous 

 membrane of mammals. 



Charles Richet, in his work entitled Du Sue Gastrlque chez I'JIonime 

 et les Animaux, proved that the gastric juice in marine fish, such as the 

 dog-fish, is almost neutral when fasting, and mucoid in character. 

 During digestion the secretion is much more acid than in man, and con- 

 tains a more active pepsin. In a dog-fish weighing 1 kilogramme he 

 obtained 5 grammes of dried gastric mucous membrane, which was 

 capable of digesting 150 grammes of egg albumin, or nearly one-sixth of 

 the total weight of the fish. In Scyllium he found the gastric acidity 

 to be as high as 0'79 per cent. HOI. 



