HEAT OF FISHES. Ill 



only in the manner in which they do. But this is not 

 the only cause, since if a fish have his head and gills im- 

 mersed in water, and the rest of his body exposed to the 

 atmosphere, he will not live but a few days. Death 

 seems to be occasioned by an excessive loss of matter 

 by transpiration from the exposed surface of the body, 

 and to a change in the pressure of the surrounding medi- 

 um, as well as to the un fitness of the gills to act upon 

 the atmosphere. 



Emily. Do tell me, Dr. B., why fishes are called 

 cold-blooded animals ? They no doubt have a certain 

 temperature which is unaffected by external changes. 



Dr. B. They are called cold-blooded because their 

 temperature is very low compared with ours, though it is 

 generally a little above that of their usual medium. The 

 standard heat of fresh water fishes is 60 ; that of those 

 of the sea, about 50. What is exceedingly singular in 

 regard to the animal heat of fishes, is that it is considera- 

 bly modified by external temperature. Mr. Hunter put 

 an eel whose heat was 44, while that of the atmosphere 

 was the same, into water heated to 65 for fifteen min- 

 utes ; upon examination at the end of that period, it was 

 found to be of the same degree of heat with the water. 

 Having put an eel, the heat in whose stomach was 37, 

 into a freezing mixture, its temperature sunk to 31 Q . 

 The animal at that time appeared dead, but next day it 

 was alive. At another time he put a living and dead eel 

 and a living and dead tench a fish not found in 

 our waters ; it belongs to the same family with the carp 

 into warm water ; they all received heat equally 

 quick, and when they were exposed to cold, both the 

 living and dead lost their heat with equal quickness. It 

 is strange too, to see in what a hot medium fishes some- 

 times live. Sonnerat declares that he saw in the Phil- 

 lipine islands, fishes swimming in water whose heat was 

 187 of Far. 



Emily. Why, an access of a few more degrees of 



