58 
DR. DAVY ON ANIMAL HEAT. 
This result seems in accordance with the inference, that all fishes are not cold- 
blooded. In the work already referred to, reasoning from the smaller size of the 
respiratory nerves of the Pelamys Sarda, compared with those of the Tunny, I offered 
the conjecture that its temperature would be found less than that of the Tunny, 
and somewhat higher than that of fishes of other orders with still smaller re- 
spiratory nerves, a conjecture which the observations described may be adduced 
as confirming. 
In connexion with their temperature, my attention was directed to the blood of 
these fishes. I have been able to examine it only in three instances, and that par- 
tially, viz. the Sword-fish, th e Pelamys Sarda, and the common Tunny. Considering 
the great difficulty there is in obtaining the subjects for experiment under favourable 
circumstances for examination, imperfect as were my results, I am induced to offer 
them now. 
The Sword-fish appears to abound less in blood than the Pelamides, and the Pela- 
mides less than the common Tunny ; and accordingly the muscles of the former 
two are of a much lighter colour than those of the latter. 
The blood of the Tunny is very rich in red particles : this is indicated not only 
by its appearance, but also by its specific gravity, which I have found as high as 1 ’ 070 . 
The blood tried was taken from a fish, caught in the sea of Marmora, that weighed 
between two and three hundred pounds. 
The blood of the Pelamides appears to be less rich in red particles than that of the 
Tunny, but more than that of the Sword-fish : I have not ascertained its specific 
gravity. The specific gravity of the blood of the Sword-fish I have found to be 1‘051 ; 
the fish from which the blood was taken was caught in the Bosphorus, in the month 
of December, and was of large size. 
Under the microscope the appearance of the red particles of the blood of these three 
fishes is very similar. They are commonly thin oval discs (very soft), containing 
oval nuclei : a few circular discs are intermixed with them. The medium dimensions 
of those of the Pelamides were about 2 Woth of an inch by 3 oVo th ; of the Sword-fish, 
about -gwoth by 4000 th ; and of the Tunny, about s ' oVo th by -g^o- 
That the red particles constitute that portion of the blood which is chiefly con- 
cerned in the production of animal heat, is now generally admitted. What a contrast 
appears, in comparing the blood of the fishes under consideration, with that of some 
of the colder, especially of the cartilaginous kind, in which it is very small in quan- 
tity, accompanied by a proportionally diminutive heart, and poor in red particles ! 
the blood of the Squalus Acanthias I have found to exceed in density only a little 
its serum, one being of the specific gravity T030, the other of the specific gravity 
1 027. 
Whether the peculiar constitution of the red particles operates in any way in pro- 
moting their union with oxygen, seems to be deserving of consideration. It may be 
thrown out as a conjecture, that the circumstance of their possessing nuclei may 
