

of the Salmon in Fresh Water. 47 



much more numerous than during the first half of the year. The mean 

 numbers in all of the three sections of the alimentary canal are the same 

 in those months when the results from the first roll-tubes are considered. 

 And it is a most noteworthy fact that in not one of the six fish from 

 which second tubes were made could a single growth be detected in the 

 cultivations from both the oesophagus and stomach, while only six 

 colonies in all, or one per fish, were obtained from the intestinal 

 contents. 



From these data it appears that there is a distinct connection between 

 the temperature and the number of organisms present in the intestinal 

 tract of the salmon caught at the mouth of fresh-water streams or in 

 the tidal estuaries. The temperature of sea-water takes much longer 

 to rise as the months advance than the temperature of the air, and the 

 great increase in the number of bacteria cultivated during the months 

 of July and August corresponds with the period of the year at which 

 the temperature of shallow waters is near its maximum. The water in 

 the rivers of Scotland, and in a considerable portion of the sea close to 

 their mouths, must be affected in spring by the melted snow from the 

 hills, with the result that the temperature of the tidal water remains 

 low. Although the fish do not feed, they must swallow some of the 

 water. 



(6) Salmon Caught in the Upper Waters. 



Twelve salmon from the upper reaches were employed for the investi- 

 gation of the number of bacteria present in the alimentary canal. They 

 fall to be divided as to the season of capture into three classes. Three 

 were caught in May and June, four in July and August, and five in the 

 months from September to November (Table III.) 



The results are depicted in Charts IV., V., and VI. in a similar way 

 to those obtained from the fish captured in tidal waters. 



It is at once apparent that the same increase in the number of 

 organisms occurred in the months of July and August, that almost no 

 colonies were obtained in May and June, and that the bacteria found in 

 the alimentary tract during the later months, though much less than in 

 late summer, were more numerous than in the fish from the river- 

 mouth (Chart IV.) 



In May and June the total number of colonies which appeared in the 

 roll-tubes was extremely small. Only twelve growths were cultivated 

 from the alimentary tracts of three fish in the first tubes, or four 

 apiece, and only four in the second tubes, all of which grew in the tubes 

 inoculated from the oesophagus. 



The increase in the numbers in July and August is shared equally by 

 the oesophagus and stomach. The number grown from the intestinal 

 contents was smaller by about three-fifths than the number in either of 

 these sections. 



hi the autumn months the drop in the figures is most marked in the 

 r;ise of the oesophagus, and least in the case of the intestine. 



The two Charts following (Charts V. and VI.), in which the organisms 

 capable of liquefying gelatine have been separated from those incapable 

 of so doing, show that the increase in the number of colonies obtained 

 from the stomach contents in July and August is due to a predominance 

 of bacteria able to dissolve gelatine. The number cultivated from the 

 stomach exceeds that obtained from the oesophagus. 



Practically no liquefying organisms were grown from any of the 

 sections during the first season, or from the intestine in the third 

 season of the year. During the last period, however, the colonies 

 from the stomach contents were numerous, those from the oesophagus 

 fewer, but still much above the number in the intestine. 



