36 Investigations on the Life-History 



5. THE BACTERIOLOGY OF THE ALIMENTARY CANAL 

 OF THE SALMON. 



A. LOCKHART GILLESPIE, M.D., F.R.C.P.ED., F.R.S.E. 



At one time it was seriously argued that the rapidity of digestion in 

 fish is due to fermentative processes induced by bacterial forms. This 

 theory was promulgated at a time when the large proportion of pepsine 

 present in the gastric secretion of fish had not been ascertained. The 

 fallacy presented by this theory is at once apparent when the time 

 necessary for the bacterial decomposition of albuminous bodies, the 

 bodies which are digested in the stomach, is considered ; and especially 

 when it is remembered that the temperature at which most bacteria 

 grow is very much above that of the inner cavities in fishes. 



The antiseptic action of an active and acid gastric juice has also been 

 demonstrated, and the general rule may be laid down that the more 

 active the gastric secretion and the greater its acidity the fewer bacteria 

 can pass unharmed into the intestine. 



Miescher Ruesch, in the paper referred to in a preceding section (II.), 

 states categorically that the salmon caught in the upper reaches of the 

 Rhine show less tendency towards early decomposition in the bowel, 

 while those caught in tidal waters soon exhibit signs of putrefaction 

 there. He adduces no detailed evicfence in support of this statement, 

 but suggests that the non-occurrence of decomposition in the intestines 

 of salmon which have ascended a river is due to the fact that they do not 

 feed, and therefore do not swallow bacteria with their food, arguing 

 further that this absence of decomposition implies a self-imposed 

 abstinence from food for some time before entering fresh water. 



The observations detailed below were undertaken for the purpose of 

 ascertaining the correctness of this statement, and to investigate the bac- 

 teriology of the alimentary canal in more detail. They include (1) an 

 estimation of the number of organisms cultivated from the alimentary 

 tract of the salmon ; (2) a rough classification of these organisms ; and 

 (3) a comparison between their numbers and form in different parts of 

 the rivers and at different times of the year. 



1. MATERIAL USED. 



Reference to Table I. shows that of the forty-one salmon employed 

 twenty -nine were captured at the mouth, and twelve, one of these a 

 kelt, in the upper reaches of the rivers : 



[TABLE. 



