EFFECTS OF GASES ON TROUT. 



359 



The last column contains the numbers of young trout in each 

 pair of boxes which subsequently developed blue-swelling. 



Consideration of this table shows several things. In the first 

 place the number of dead eggs is abnormally large even in the fifth 

 pair of boxes. This is certainly due to overcrowding. The practice 

 of the fish hatchery has been to put only about 2000 eggs in a box, 

 and here there were 7500. This was done intentionally with a view 

 to producing a high death rate. In the second place it shows that 

 fewer eggs die as the water, by rippling and falling, loses nitrogen, 

 gains oxygen, and loses radium emanation, and in fact becomes more 

 like water exposed freely to the air for a considerable time. If the 

 number of the eggs dying in the upper box be called 100 and the 

 radium emanation in the pair be also taken as 100, and the number 

 for the other boxes be reduced correspondingly a rather striking 

 similitude exhibits itself thus : — 



The table does not, however, shew, at any rate markedly and 

 conclusively, that blue-swelling is also a disease dependent on 

 aeration, but experiments now to be described show this. 



The results just given were obtained in the winter of 1909 

 during the trout hatching season in June and July, and no further 

 opportunity for further work occurred until the hatching season in 

 1910. This year we were fortunate in finding two wells closely 

 adjacent to one another, and yet possessing an entirely different 

 radium emanation content. We made a careful examination to 

 ascertain if there were any differences in the amounts of the other 

 dissolved gases, with the results which will be given. One of these 

 wells was that previously used, and the other supplied a set of eight 

 pairs of boxes. In these experiments, however, only one side of the 

 set of boxes was generally used. If any eggs were put in the other 

 box of a pair the figures for these are given in brackets. The result 

 of experiments with these two wells are given below in tabular form.i 



1 Farr and McLeod, Trans. N. Z. Inst. 1910, p. 56. 



