
DR DAVY’S OBSERVATIONS ON THE CHARR. 329 
As a solution of common salt has the property not only of keeping liquid the 
fluid of the yolk, but also of dissolving its coagulum, it seems well adapted as a 
medium for the purpose of examining the foetal structure. Using it thus, I found 
that an ovum in which the embryo was active on the 42d day, immersed in a 
solution of salt of the specific gravity 1033, kept therein about half an hour, 
retained its vitality ; and that, excluded by an opening artificially made in the 
shell, the young fish remaining in the solution, continued active for another half 
hour. This result led me to try the effect of keeping the ova in solutions of com- 
mon salt, and also the young fish, to ascertain whether the former would be 
hatched, and what would be the effects on the latter. One trial was made with 
the ova, using salt water of the specific gravity mentioned, 1033 ; another with 
water just perceptibly impregnated with salt, confined in glass bottles and kept 
in the room of the average temperature of about 55°. In the stronger solution, 
the ova remained transparent, but no marks of development appeared. In the 
weaker solution, on the 26th of November,—the trial was begun on the 4th,— 
black specks denoting eyes, in the act of forming, were observable in four ova, 
and vessels carrying red blood in the vitelline membrane. In this stage, further 
progress was arrested by death. The first experiment on a young fish was made 
on one that had been hatched about 22 days. Put into sea-water, diluted with 
spring-water so as to be of specific gravity 1020, it was found dead three hours 
after; it was contracted in length from ‘68 to -46 of an inch. The next was on 
a young charr of the same age: this, immersed in a solution of the specific gravity 
10036, after 24 hours, seemed as active as before. More salt was then added so 
as to increase the specific gravity to 10068, but still without marked effect. 
After other 24 hours the specific gravity, by another addition of salt, was raised 
to 10098 ; now the fish became more restless, as if seeking to escape. After the 
same interval a fresh portion of salt was introduced, raising the specific gravity 
to 10153: the effect now was strongly marked ; in about six hours the fish was 
found motionless, except the lower jaw, which, under the microscope, exhibited a 
tremulous movement, and except the heart, which still acted pretty vigorously, 
and which continued to act, but with decreasing force, for about 20 hours, reckon- 
ing from the time that the fish first appeared motionless and moribund. 
The next trials I shall mention were made with the intent to endeavour to 
ascertain how long young charr might be kept alive in the same portion of water, 
and that a small quantity, such as might be used in conveying the fish from place 
to place at an early age, when, before the yolk is exhausted, it stands in no need of 
a supply of food from without. Two experiments were made, one with a portion 
of pure oxygen over the water, the other with common air. The volume of water 
and air in each instance was nearly equal—about four ounce measures,—the 
capacity of the containing bottle being about eight ounces. The bottles, after 
the introduction of the young fish, were closed with a glass stopper and inverted 
VOL. XX. PART III. 4£U 
