The vesicular lungs of that reptile, as v/ell as of all oviparous quadru- 

 peds, are much more irritable than those of warm-blooded animals; they 

 appear to contract, at the will of the animal. The frog is without a dia- 

 phragm, attracts the air into its lungs, by swallowing it by a real process 

 of deglutition, as was proved by Professor Rafn, of Copenhagen, who 

 killed those animals by holding their jaws asunder for a certain time, 

 They reject the air by a contraction of the lungs, in the same manner as 

 in man, the bladder empties itself of urine. 



In birds, whose diaphragm is equally membranous, and contains seve- 

 ral openings to transmit the air into the pulmonary appendices, the pari- 

 etes of the thorax are likewise more moveable than in man and quadru- 

 peds. Their pectoral muscles are more powerful, their ribs contain a 

 joint situated in the middle of those arches, which are completely ossified 

 in that class of animals ; and those two portions move on each other, 

 forming, at their point of union, angles more or less acute, according to 

 the distance of the sternum from the vertebral column. 



A numerous class of cold red-blooded animals, viz. fishes, have no 

 lungs; the gills, which supply their place, are small penniform lamina, 

 generally four in number, situated on each side, at the posterior and late- 

 ral part of the head, covered over by a moveable lid, to which naturalists 

 give the name of operculum. The water which the animal swallows; 

 passes, when he chooses, through the parietes of the pharynx, which 

 contain several considerable openings, is spread over the gills and 

 the pulmonary vessels which are distributed in them, then escapes at the 

 auricular apertures, when the animal closes his mouth, and raises the 

 opercula. It is not known, whether the water is decomposed and yields 

 its oxygen to the blood which circulates in the gills, or whether the 

 small quantity of air that is dissolved in the water, alone serves to vivify 

 the pulmonary blood. The latter opinion seems the most probable, if it 

 be considered that a fish may be suffocated, by closing accurately the 

 vessel of water in which it is enclosed. The same result might, I con- 

 ceive be obtained, by placing the vessel under the receiver of an air- 

 pump, so as to exhaust it completely. 



Respiration, which is completely under the influence of the brain, as 

 far as relates to its mechanism, is less dependent upon it, in regard to the 

 action of the lungs on the blood, and the combination of that fluid with 

 oxygen, which is the essential object of that function. The nerves, 

 however, have some influence on that function, as well as on the various 

 secretions, in which, according to Bordeu, they are of the first rate im- 

 portance. Dupuytren ascertained by his experiments, that the divi- 

 sion of the cervical portion of the eighth pair of nerves, did not sensi- 

 bly affect respiration; but the animal died with all the symptoms of as- 

 phyxia, when this nerve was divided on both sides. Death took place, 

 in the course of a few minutes, when the experiment was performed on 

 horses. Other animals did not die so soon after ; dogs, for instance, have 

 been known to live several days after the experiment. By interrupting 

 the communication between the lungs and the brain, we paralyze the for- 

 mer of these organs, and it ceases to convert the venous into arterial 

 blood. This fluid, conveyed by the pulmonary artery, continues of a dark 

 colour, when brought to the left cavities of the heart; the arteries con- 

 vey the blood without its having received its vivifying principle, in pass- 

 ing through the lungs which are paralyzed, by having their nerves tied 

 or divided. It is easy to conceive that all organs, for want of the stimu- 



