of the Salmon i/i Fresh Water. 51 



it. From each fish 321 colonies were obtained, or an average of 107 

 from each section of the alimentary canal. 



In March the average number of colonies obtained from all parts of the 

 ti-.ict was 62 ; in May and June, 13-7 ; in July and August, 697 ; and 

 September to November, 255. It is difficult to account for the larger 

 number obtained from the fish caught at the river mouths in March 

 than from those captured during May and June, especially as during the 

 latter month several of the fish came from the higher reaches. 



CONCLUSIONS. 



From these observations it would appear that the alimentary tract of 

 the salmon in tidal waters, preparatory to ascent of the rivers, contains 

 a smaller number of bacteria than the tract of those fish which have 

 proceeded up the streams. The number of growths obtained from the 

 oesophagus of the lower fish is below that found in the upper fish (27 per 

 cent.), from which fact it may be concluded that fewer organisms are 

 swallowed, but that the difference is not very great. The greatest 

 contrast between the results for the two classes of fish is presented by 

 the figures for the growths cultivated from the stomachs. Fewer 

 colonies were obtained from the stomachs of the lower-water fish 

 than of the upper, while the liquefying bacteria formed the larger part 

 of the colonies in the case of the upper fish. 



Mie.scher Ruesch affirms the exact opposite. He finds that the salmon, 

 from the upper reaches do not decompose so quickly as the lower fish; 

 due, he suggests, to the small number of organisms swallowed by the 

 upper fish while fasting. Direct experiment shows that the 

 putrefactive bacteria are more numerous in the upper fish than in the 

 lower, as well as affording evidence of the greater number of all bacterial 

 forms in these fish. Although the upper-water salmon may not feed, 

 they must swallow some of the water of the streams more or less 

 frequently. The variations observed are most probably due to the pro- 

 portion of organisms in the surrounding water more numerous in the 

 fresh water than in the tidal waters, and consisting of a greater number of 

 liquefying or putrefactive forms. That the diminution in the numbers of 

 organisms in the alimentary canal below the (esophagus is much more 

 O>arked in the lower fish than in the upper cannot be due to any in- 

 creased effect of gastric digestion, is shown by the smaller percentage of 

 albumin digested by their extracts. The acidity, however, of the gastric 

 extracts of the lower fish is slightly in excess of the acidity found in the 

 upper salmon ; while the number of non-liquefying colonies, although 

 actually less numerous, are, relatively to the total, in a much higher 

 proportion. 



These facts seem to lead to the following conclusions : 



1. Fewer organisms are swallowed by salmon in tidal waters. 



2. A larger proportion of these organisms are non-putrefactive and 

 acid-forming. 



3. The presence of these non-putrefactive organisms in excess of the 

 liquefying forms prevents the rapid growth of the latter. 



4. As the members of the putrefactive class of bacteria grow much 

 more quickly than the bacteria forming the other class, fewer colonies 

 can be obtained from each part of the canal. 



5. The proportion between the total number of organisms grown from 

 the stomach and intestine in the lower and upper fish did not differ so 

 much in the warm summer months as during the late autumn, when 

 the colonies, grown from these sections in tne upper fish, largely 

 exceeded the number grown from those in the fish caught at the mouth. 



6. Of all the fish examined, the organisms weie very much more 



