43 



no comparative experiments on the blood of the. 

 brute creation; and of this, Animal Chemistry 

 has taught us nothing beyond the external cha- 

 racters, which, in Zoology, constitute a part of 

 the distinctions of the different classes of animals. 

 On the respiration of birds, and amphibia, no 

 experiments have been made. We only know, 

 that, birds are exceedingly delicate as to air, 

 and that in the same atmosphere in which a bird 

 dies, a mouse may live without any perceptible 

 inconvenience. On the respiration of fishes, we 

 are furnished with more experiments. It is cer- 

 tain, that the fish oxidates its blood in the gills, 

 at the expence of the oxygene gas, which the 

 water contains to the amount of about TOT? of its 

 volume. But this kind of respiration is not of so 

 much consequence to fish, as to the mammalia, 

 since fishes may continue alive for several days 

 in water, which is void of ^air; but they die at 

 last, if air is not admitted, and it cannot be ob- 

 served, that the least decomposition of the water 

 takes place by their respiration. Fishes have a 

 vessel, which is called the air bladder, and which 

 has, though probably not correctly, been consi- 

 dered as partaking in the operations of the gills 

 on the blood, whereas it seems intended to regu- 

 late the specific weight of fish, so that it may, 



