of the Salmon in Fresh Water. 49 



Table showing the number of Mia'o-Organisms grown from different 

 sections of the Alimentary Canal in Salmon caught in the Estuaries 

 and in the Upper Waters: 





The proportion between the number of colonies found in the tubes 

 made from the oesophagus from July to November in the fish 

 from the upper reaches and the mouths of the rivers differ only slightly. 

 The number of colonies cultivated in autumn from the stomach 

 contents of the fish from the upper waters exceeds that of the 

 lower fish by 64 per cent, of its total, against 54 per cent, similarly 

 found in the summer fish. In like manner in autumn the excess of 

 organisms grown from the intestines of the upper-water fish over those 

 found in the fish from the estuaries constitutes 42'5 per cent, of their 

 number, compared with an excess of 28*9 per cent, from the same part 

 of the canal in the summer fish. 



The only season in which the figures for the average number of 

 colonies grown from the alimentary canal of the salmon from the upper 

 parts of the rivers are less than those for the fish from the mouths is 

 that of May and June. During these months the excess in the number 

 of organisms grown from the fish caught at the mouth over the number 

 found in the others amounts to over 90 per cent, of the first number in 

 all parts of the digestive tract. 



We may further say, then, that in early summer the bacteria 

 present in the alimentary tract of the salmon are less numerous when 

 the fish is in the higher reaches of rivers than when it is still in tidal 

 waters. On the other hand, the upper-water fish caught during 

 the next two months are characterised by a much greater increase in 

 the number of bacteria present in their alimentary canals, and conse- 

 quently show a marked excess in actual numbers of bacteria over those 

 in the fish at the river mouth. In the following months the rate of 

 decrease in the number of bacteria present is greater in the fish in 

 tidal waters, so that, although the organisms in the upper fish are not 

 nearly so numerous as in the preceding periods, the proportional excess 

 of bacteria in the upper- water fish over the number in those from the 

 mouth is increased. 



The number of organisms in the mucus in the cesophageal tube 

 is practically the same in both sets of fish in May and June, but shows 



