Dr Davy on Animal Heat. 353 



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 ^Jih of an 

 inch by —fh. ; of the Sword-fish, about ^th by ^1 th ; and of 

 the Tunny, about ^th by s^^h- 



That the red particles constitute that portion of the blood 

 which is chiefly concerned in the production of animal heat, 

 is now generally admitted. What a contrast appears, in com- 

 paring 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 quantity, accompanied by a propor- 

 tionally 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 1.030, 

 the other of the specific gravity 1.027- 



Whether the peculiar constitution of the red particles ope- 

 rates in any way in promoting 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 have an efi^ect of the kind, supposing, which is possible, 

 the blood corpuscle and nucleus, or containing and contained 

 pai't, to be in the electrical relation to each other of positive 

 and negative. If it be objected to this, that, as regards nuclei 

 as well as size, there is an analogy between the blood-corpuscle 

 of fishes, birds, and reptiles, the temperature of which com- 



