16 TROUT FISHING 



follows that in order to feed, he has a labour to per- 

 form proportionate to the resistance of the stream 

 he is in. We see but few places in rapid streams 

 of rocky bottoms to which the fish can retreat 

 to evade the powerful current, or these so small, 

 that a single stroke of his tail brings him into the 

 current necessitating increased labour, so that in 

 short by far the greater part of fish inhabiting these 

 precipitous streams are incessantly performing 

 great muscular exertion ; it is evident then that as 

 the muscles moving their bodies and fins are con- 

 stantly exercised, and that no muscular contraction 

 can take place without wear and tear of tissue, the 

 trout must either very speedily suffer from exhaus- 

 tion, or supply his body with materials for fresh 

 blood for the new formation of changing parts, and 

 this supply must be proportionate to his labours 

 and in the same ratio as the frequency of repeti- 

 tion of his labours. He cannot take a large meal 

 and quietly retire to rest for its digestion, since 

 in obtaining each portion of that meal, and a 

 prolonged one too, he is in violent exertion, is 

 wearing away and reforming his tissues, and at 

 the same time hastening the digestion of the hard- 

 earned meal, and moreover, when satiated, if so he 

 could be, he has literally no place to retreat to 

 where he could be free from labour, though per- 

 haps lessened in some degree in some spots it 

 might be. Now this is quite the case with by 

 far the majority of trout in small rapid streams ; 

 constantly working*, constantly feeding, sometimes 

 more, sometimes less, now feeding on one insect 



