HISTORY OF THE WORKS OF CUVIER. 151 



The mode of respinition is in constant dependence on tlie circulation, wliicli car- 

 lies tlie blood to the air, or to the organ which receives the air ; the force of the 

 movements is in constant dependence on the quantity of the respiration, for it is 

 resiiiration which restores to the muscular fibre its exhausted irritability. 



The quantity of respiration everywhere determines the vigor, the rapidity, and 

 the kind of movement. The movement which requires most muscular energy is 

 that of flying, and the bird has a double respiration. The mammal has move- 

 ments more limited, and it has a simple res])iration. The reptile has movements 

 more feeble still, and it has but an incomplete ]'espiration. Tlie bird respires 

 not alone by its lungs, but by its whole body. The air, after having traversed 

 the lungs, which are transpierced like a sieve, penetrates into the cellules of the 

 abdomen, into the cavities of the bones, &c. It is, therefore, not alone the blood 

 of tht lungs, but the blood of the whole body, which respires. The mammal has 

 but a simple respiration, for there is but the blood of its lungs which respires; 

 but this simple resjiiration is complete, for all the blood of the body passes 

 through the lungs before returning to the members.- Finally, the reptiles have 

 but an incomplete respiration ; their pulmonary circulation is only a fraction of 

 the general circulation ; there is but a part of their blood which respires, or 

 which, retiu'ning from the members to the heart, })asses from the heart to the 

 lungs before returning to the members. Hence, the reptiles have only cold blood, 

 only slow movements, interrupted by long repose ; they are all subject to hiber- 

 nating torpor, &c. On the other hand, iish have a complete pulmonary circu- 

 lation ; but they have only an aquatic respiration, that is to say, an imperfect 

 one, since they have, for respiring, only the small quantity of air contained in the 

 water ; quite the contrary of what has been just said of reptiles, which have an 

 aerial or perfect respiration, and an incomplete pulmonary circulation. 



IS'ow, these two things are mutually conipi.'usatory : an aerial or perfect respi- 

 ration is compensated by an incomplete })ulmonary circiilation, and a complete 

 pulmonary circulation by an aquatic or imperfect res})iration. Fish, therefore, 

 have only cohl blood, like the reptiles — only movements which require little 

 nuiscular energy, &;c. Thus, there are in vertobrato animals four definite degrees 

 of respiration : the complex respiration of birds, the simple but complete respi- 

 ration of mammals, and the incomplete respiration, incomplete by two diilerent 

 means, of reptiles and fishes. And there are four kinds of movements which 

 correspond to these four degrees of respiration : the flight of the bird, which cor- 

 responds to the duplicate respiration ; the step, the leap, the run of mammals, 

 which correspond to the complete, but single resi)iration ; the crawling of the 

 reptile, a movement by which the animal does no more than drag itself along 

 the earth ; and the swimming of the fish, a nKJveinent for which the animal ha? 

 need of being sustained in a liquid, the specific gravity of which is nearly equal 

 to its own. And as of movement, so too of digestion. The greater the capacity 

 of res})iration, the more rapid the digestion. The most rapid digestion is that 

 of the bird, the slowest that of the rejjtile ; the bird surprises us by the frequency 

 of its repasts, the rej)lile l)y the duration of its abstinences. 



Everything in the l)ird is formed for flight. It required a wing of wide sur- 

 face to strike tlie air; for this wing large nmscles were needed to move it ; these 

 muscles required very large bones for their insertion. And tlu; bird has a sternim? 

 developed into a salient blade, into a crest, it has a pectoral muscle iclatively 

 enormous, &c. So much for the exterior; internally, it has a duplicate respira- 

 tion, an animal heat and muscular energy which correspond to that icspiration ; 

 and, for this duplicate respiration, it has limgs perhn-ated like a sieve, air-cells, 

 which are the appendix of its lungs, &c. Nor did all this sulHce ; my own exper- 

 iments have shown that the brain is comjxjsed of three parts essentially 

 distinct:* the cerebrum, exclusive seat of intelligence; \\\o cerebellum, seat of the 



* See Diy llcchtrchts txpirimntlalcs sur ks jjropTi6l6s ct Its fonclions du sysi^iiie ncrvtux, 

 &c. Second edition, Paris, ld42. -^ 



