THE BREEDING SALMON. 505 



were only twenty-five miles a day, the fish must make their way through 

 two thousand miles of water. In fact, however, the Khine is through- 

 out much of its course a swift flowing river, leaving Switzerland at a 

 speed of four or five miles an hour; and the spawning grounds of the 

 salmon lie above the falls and rapids south of Basel. Indeed even these 

 considerations can scarcely be taken as a measure of the physical ex- 

 ertions of the salmon, since the swifter the current the greater becomes 

 their activity. The heaviest runs of the salmon occur during June and 

 July, although many fish whose condition shows them fresh from the 

 sea are taken at Basel even during January. All these fish remain near 

 the head of the river through the spawning season, and in the follow- 

 ing December unite in a headlong rush back to salt water. The average 

 duration of their stay in the Ehine is therefore from six to nine 

 months, while in some cases as many as fifteen months must elapse 

 from the day the salmon enter the mouth of the river until their return 

 to the sea. 



In view of these facts it would seem almost beyond belief, had not 

 Miescher established it by absolutely complete demonstration, that the 

 salmon never feed in fresh water. From the day they leave salt water 

 until they return to it they maintain an absolutely unbroken fast. 

 Careful examination of more than three hundred fish caught at Basel 

 at all periods of the year, and of many taken in the lower reaches of the 

 river just after the fish had left the sea, showed that not only was the 

 alimentary canal empty of all food material, but the digestive apparatus 

 was in no condition to handle nutriment even if offered it. The gastric 

 mucosa was in a more or less desquamated condition, and alkaline in 

 reaction. The gall bladder was empty, and the pancreas shrunken. 

 Only two exceptions were noted, and these more apparent than real. 

 In the stomach of one fish was found a large winged insect — quite un- 

 digested; in another a minnow — only partially digested. Of the 

 latter case, however, Miescher records that the fish was caught near 

 Basel in January, long after the spa\vning season, and was so extremely 

 emaciated as to suggest that it must have been prevented in some way 

 from escaping back to the sea. 



The development of the genitalia (or sexual glands), occurring 

 almost wholly after the salmon have entered fresh water, becomes of 

 the greatest interest in the light of these observations ; for the material 

 built up in these organs must be drawn from the other tissues of the 

 animal itself. To the problems involved in these tissue changes, as 

 well as to those resulting from the expenditure of energy by the fish 

 in their long journey up stream, Miescher devoted himself especially. 

 His examinations and analyses of the salmon caught in the lower 

 reaches of the Ehine at all periods of the year, and of those taken at 

 Basel from January to I^Iay, show that the fish on their way up stream 



