EFFECTS OF GASES ON TROUT. 361 



either to eggs or newly-hatched trout, that difference must be 

 ascribable either to radium emanation or to oxygen. In the first 

 and fifth columns of the table relating to each well will be found 

 headings marked "Eggs" and "Blue-swelling." These columns 

 give the number of eggs dying before hatching and the number of 

 cases of blue-swelling subsequently developed in the yolk sac stage 

 when 2,000 healthy brown trout ova from river fish were put in the 

 box to which the figure refers. The results are therefore comparable. 

 Now, I think, it will be seen that whilst there may be a decrease in 

 the number of dead eggs as we go from box to box in the series 

 supplied from well No. 1, yet it cannot be said that there is such 

 a decrease in the series of boxes supplied by well No. 2. The 

 difference is not marked, and may be accidental, but taken in con- 

 junction with the previously-given figure relating to the egg dying 

 from well No. 1, where the decrease in mortality was, most 

 marked, the figures point conclusively to the fact that a large number 

 of eggs die in the hatching boxes owing to the water being insuffi- 

 ciently aerated, whatever we may mean exactly by that expression. 



Now, turning to column five in the two wells, viz., that headed 

 " blue-swelling," I do not think it can be doubted but that the 

 figures show a marked difference. In Well No. 1 they began with 

 70, with a check in the parallel box of 72 ; in the fifth box they fall 

 to 29 with a check of 28 Indeed we have no right to expect such 

 an evenly decreasing series of figures as were obtained. On the 

 other hand, over the series of eight boxes in No. 2 well, cases of 

 blue-swelling amongst young trout hatched from these 2000 

 brown trout eggs hardly show any variation at all. It maybe con- 

 sidered, however, the last column of each well, which is also headed 

 blue-swelling, whilst they support the conclusion that blue-swelling 

 is a disease that is due to want of " jeration," do not enable us to 

 reject " excess of nitrogen " from the meaning of that expression. 

 These series of results, however, were from a very different class 

 of fish from the others. They refer to 2500 rainbow trout fry, a 

 " pond " fish, and one much more delicate than brown trout. By 

 a pond fish is meant that the eggs from which these fry were 

 obtained were stripped from fish kept in confinement in the hatching 

 pond, whereas the brown trout eggs were obtained from fish in- 

 habiting rapidly flowing streams. Besides, whilst the brown trout 

 eggs refer actually to the hatching from 2000 ova, the numbers of 

 rainbow fry actually placed in the boxes of No. 2 well were, owing 

 to scarcity of fry, only 1000, and the results were multiplied by 2.5 

 to make them comparable with No. 1 well. The figures, therefore, 

 in this the sixth column for each of the two wells are for the first 

 of the reasons given above not at all comparable with the figure in 

 the fifth column for the same well, and for the second reason the 

 figures in the sixth column of the two wells are not strictly com- 

 parable with each other.. 



The conclusions arrived at in this paper are as follow. There 

 is abundant evidence (not all given here) to show that there are 



