PRACTICAL FISH-CULTURE. 573 



poured over the whole mixture, and the whole was stirred immediately. 

 The pouriug-over of the water and the stirring was, if possible, done 

 simultaneously, almost suddenly.* 



The result of experiment jS^o. 1 was a failure. 



Of Nos. 2 and 3, only a few eg-gs out of several thousands developed, 

 so that these two methods must likewise be considered failures. 



In No 4, all the eggs were regularly developed with but very few ex- 

 ceptions. This method must therefore in every way be considered a 

 success. It was proved conclusively that ri})e eggs fresh from the fisb 

 when brought into contact with water immediately swell to such a 

 degree that the sticky layer surrounding the eggs prevents the sperma- 

 tozoa from entering the interior of the egg, impregnation thus becom- 

 ing impossible. It is likewise proved almost to a certainty that during 

 the natural spawning-process of the " nase," the milt touches the roe 

 outside of the water, and that the water completes the begun process of 

 impregnation. 



This may therefore well be called natu)'e''s own method of dry Imprcgna- 

 tton. 



I have at the same time, with many other comparative experiments, 

 very frequently employed this " dry " method, especially with salmon- 

 trout, and have in all cases been successful. 



To insure complete success, the following rules and precautions must 

 be observed : 



1. The vessel used should be as flat as possible, and should, by rub- 

 bing it with a cloth, be completely freed from any dripping water ; the 

 inside of the vessel may remain a little damp. 



2. As the temperature of the air but rarely corresponds with the tem- 

 perature of the water, the vessel should externally, for some time, be 

 brought into contact with the water to be used for spawning. This 

 should be done so long before i)ouriug in the roe as the length of time 

 required for equalizing the temperature throughout the whole body of 

 the vessel. If the difference between the temijerature of the air and 

 the water is not very great, neglecting this precaution will not prove 

 injurious. It should, however, never be neglected when these tempera- 

 tures differ greatly, or when the temperature of the air is below 0°, 

 (Reaumur.) The vessels should not be taken out of the water before 

 the end of the above-mentioned period. 



3. PJace in readiness both the fish, the one containing the roe and the 

 one containing the milt. 



4. First carefully dry with a cloth the fish containing the roe, avoid- 

 ing the slightest pressure," so as to prevent the premature emission of 

 the loose spawn ; hold the fish in a horizontal xjosition, and dry your 



* The claim made on pages 541-543, for the discovery of a literally dry method of 

 impregnation by American fish cnlturists, ■will have to he abandoned in favor of 

 European specialists. It -will be seen by reference to pp. 515 and 577 that Dr. Voiigf, 

 cf Switzerland, and Professor Eusch, of Norway, have adopted similar methods. 



