POLLUTIONS OF WATER— HOW EGGS IMBIBE GASES. 39 



Irrespeetivo of sediments occasioning destruction to the eggs, and concerning 

 ■which the foregoing shows the general cause, there are pollutions more or less 

 poisoning the water, and which if sufficiently potent of course destroy the 

 vitality of the eggs, or perhaps occasion the young to be a sickly race. Some 

 pollutions, however, may be present which do not act in so direct a manner, such 

 as paraffin. Doubtless this product of wood-oil or tar-oil stearin, when in a pure 

 state, is inodorous, tasteless, and insoluble in water ; but in its commercial 

 condition, as used in lamps and employed in the following experiments,* its 

 odour was pretty strong. It would, however, seem that in a strong flow of water, 

 especially when of moderate depth, this oU floats away without being immediately 

 fatal, although very injurious, to incubating salmonoid eggs : while I have 

 known it accidentally tried on a large scale where a good current of water was 

 present, but the ova hatched fairly well, it being only when the flow became 

 weak that the eggs appeared to sufEer. 



Although in fish-culture a good and sufficient stream of water is considered 

 highly desirable, and that the depth above salmonoid eggs should be at least from 

 one to one and a quarter inches, such is not indispensable for incubation, as they 

 may be hatched in water in which there is but a slight current, as well as in that 

 which is only occasionally changed, or even in damp moss, and this brings one 

 directly to the question of what are the changes occurring that enable the impreg- 

 nated egg to exist ? Two theories have been held, the first by Vogt, that aerated 

 water obtains access through the shell of the egg to the embryo, when the carbon 

 conjoins with the oxygen of the contained air and passes off as carbonic acid gas. 

 The second theory is that the oxygen gas alone obtains access through the shell 

 of the egg, and then conjoins with the carbon. Whichever is the correct theory, 

 it is evident that the excretion of carbon must take place, or the embryo will 

 die. Likewise that, even if carbonic acid is given off, it must not remain in the 

 vicinity of the ovum, which its presence would poison. It has been pointed out 



7J lb. were placed in large masses in 18J gallons of water, which was filled up twice or thrice 

 daily. The water was led from this in the usual manner to a hatching-tray, where on December 

 15th, 1885, 230 eggs were placed, from these some were from time to time removed, but 91 were 

 treated continuously in this manner until February 22nd, or for sixty-nine days, when they were 

 transferred to clean water, and commenced hatching on March 27th, at the same time as the 

 eggs which had been thus treated from the first. Of the foregoing 91 eggs 45 were hatched, the 

 young being rather smaller and thinner than those entirely incubated in fresh water. Possibly 

 one reason they were not suffocated was that every now and then the eggs were washed by 

 means of a watering-can, a process which otherwise was doubtless destructive to some or injurious 

 to others {see Hog-backed trout). The amount of peat remaining in the reservoir on February 

 22nd was 1^ lb., consequently 55 lb. had passed over the eggs, or been lost in the amount of 

 3830 gallons of water which was consumed. The experiment was varied to see whether spates of 

 peaty water would or would not have the same influence on the eggs as a continuous flow of it. 

 On December 30th, some of the above ova were transferred to a hatching-tray supplied by clean 

 water, which would have been equivalent to their having been subjected to the spate of fifteen 

 days' duration in a peaty stream. Having been there 22 days I took some to my friend 

 Mr. E. Wethered, who most kindly photographed them when under the microscope, as well as others 

 kept all the time in fresh water, or in a peaty solution. The difference between these embryos 

 was very apparent. Those treated from the first in fresh water were normal ; such as had 

 experienced the fifteen days' spate of peat water were soft and badly developed, so that it was with 

 the greatest difficulty that any photograph of them could be obtained ; while the embryos kept con- 

 tinuously in peaty water could not be taken at all, they almost seemed to melt away. On March 

 18th, successful photographs were made of embryos in those developed in fresh water, the 

 interspace between the eyes equalled the horizontal diameter of that organ, whereas such as had 

 been exposed to a fifteen days' spate had large eyes, and the distance between them only equalled 

 one-third of their horizontal diameter, showing badly developed heads and extraordinary large eyes, 

 and although in these last the embryos lived nearly to the period for hatching, none were 

 sufficiently robust to emerge from their shells, for although some came out partially, none did 

 entirely ; they died in the process. . . i. . . 



* January 13th, 1886, at Cheltenham, a bucket was fitted with a wooden tap, near its bottom, 

 and then filled with spring water, into which 12 drops of paraffin were added to each quart, and 

 15 trout eggs were placed in a small hatching-tray, into which the water from the bucket slowly 

 dropped. On the 16th they were removed to clean water, but none lived to hatch. This was 

 repeated several times, and the average number of eggs that hatched was one in ten. The final 

 experiment was made on Feb. 3rd, and continued until the 11th ; ten eggs were employed, and 

 the paraffin was gradually augmented up to 22 drops to every quart of water. One egg died 

 March 27th, one hatched March 28th, but the remainder died. 



