IN RELATION TO THE DISTRIBUTION OF SPECIES. 
27 
in about a quarter of an hour it ceased to act. The following morning the fish had 
a sodden appearance, and its disinteg'ration had commenced. 
11. A young fish was put into water at 80°; after three hours, when the tempera- 
ture had risen to 85°, it appeared to be dead; its body was bent and it had become 
pallid. Under the microscope the heart was seen acting feebly, and the circulation 
was pi’oportionably languid. On the following day the body had become unbent ; 
the circulation in the tail had ceased, but the heart was still acting feebly. Two days 
later the heart’s action had ceased, and the only vestige of life was indicated by a just 
perceptible motion of the lower jaw, which was protracted three days longer. 
12. A young fish was kept in water gradually rising from 78° to 88° for three hours. 
At 85°, the heart acting, no circulation was perceptible in the tail ; at 88° the body 
had become bent and pale, and the heart’s action arrested. 
V. Of the Effect of Salt and Brackish Water. 
1. An active young fish and an ovum in which the circulation was vigorous, were 
put into a solution of common salt of the specific gravity 1026, which it may be 
conjectured is nearly the degree of saltness of the sea at the estuaries of our salmon 
rivers. The fish immediately became restless, and the heart’s action accelerated. 
At the end of five hours it appeared to be dying; the heart’s action had become so 
languid as not to suffice for the circulation ; notwithstanding, life was not entirely 
extinct, as was indicated by a feeble motion of the lower jaw, till about forty-eight 
hours from the commencement of the experiment. The dead fish was colourless and 
contracted in all its dimensions, and shortened at least one-third of its length. 
The effect of the salt water on the ovum was equally fatal, but judging from the 
circulation, life was protracted in it a few hours longer. 
2. An active young fish was put into a solution of common salt of the specific 
gravity 1016. It lived about four days, the heart’s action gradually becoming feebler 
till the circulation ceased. When dead there was an accumulation of blood in the 
large vessels, and, as in the former instance, a diminution of the bulk of the fish, as 
if from contraction. The saline solution, it may be remarked, was changed daily so 
as to be sure that death was not owing to, or had been hastened by, deficiency 
of air. 
3. A young fish was put into a solution of salt reduced to the specific gravity 1007, 
so as to be only slightly brackish. Immediately on immersion it showed great rest- 
lessness and increased activity, which continued with little abatement for several 
days. It has now been in the solution ten days. During the two last its activity 
has diminished, and at times it has appeared to be dying. It is rather more changed 
in form than the fish of the same age left in spring water, and the vitelline sack is 
decidedly more diminished, as if from increased vascular action produced by the 
stimulus imparted by the solution. 
4. An ovum from the Dee, the circulation in which was active, was put into saline 
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