182 



extent and capacity of the lungs, the more frequent is respiration, and 

 the greater the warmth and vivacity of animals. Birds, whose lungs ex- 

 tend into the abdomen by various membranous sacs, and whose bones are 

 hollow, and communicate with the lungs, consume a great deal of oxy- 

 gen, either on account of the magnitude of this respiratory apparatus, 

 or from their frequent, and, at times, hurried respiration. On that ac- 

 count, the habitual temperature of their body, exceeds that of man and 

 mammiferous animals. In reptiles, on the contrary, whose vesicular 

 lungs admit but a very small quantity of blood, and present to the atmo- 

 sphere a surface of very limited extent, and in which respiration is per- 

 formed with intervals of longer duration, the body is at a temperature 

 which, naturally, never rises above seven or eight degrees. 



LXXVII. Though the temperature or warmth of the body is generally 

 proportioned to the extent of respiration, to the quantity of blood exposed, 

 in a given time, to the action of the atmospherical air, it may be higher 

 or lower, according to the degree of the vital energy of the lungs. 

 These organs should not \yp considered as mere chemical receivers : 

 they act on the air, digest it, as the ancients said, anil combine it with the 

 blood, by a power which is peculiar to them*. If it were otherwise, 

 there would be nothing to prevent a dead body from being restored to 

 life, by inflating with oxygen its pulmonary tissue. The ancients alluded 

 to this action of the lungs on the air we breathe, by calling that air the 

 pabulum vitx. Its digestion was, they thought, effected in the lungs, in 

 the same manner as the digestion in the stomach, of other aliments less 

 essential to life, and whose privation may be borne for a certain time, 

 while life is endangered, when the aeriform nutriment ceases to be fur- 

 nished to the lungs, for the short space of a few minutes. 



In proof of the vitality of the lungs, and of the share which they have 

 in producing the changes which the blood undergoes in passing through 

 them, I may mention the experiment which proves that an animal placed 

 under a vessel filled with oxygen, and breathing that gas in a pure state, 

 consumes no more of it, than if it was received into the chest, mixed with 

 other gases unfit for respiration. A guinea pigi placed under a vessel 

 full of vital air and of known capacity, will live four times longer than if 

 the vessel contained atmospherical air. No remarkable difference is at 

 first perceived in the act of respiration, but if the animal remains long 

 immersed in the oxygen, his respiration becomes more frequent his cir- 

 culation more rapid, all the vital functions are executed with more ener- 

 gy. The lungs separate, by a. power inherent in themselves, the two at- 

 mospherical gases, and this process is effected by a considerable 

 power, for oxygen, in its combination with the blood, is, with difficulty, 

 separated from azote. Inifact, the blood, though in thin layers, becomes 

 dark, when exposed to the atmospherical air. 



It is observed, that the purity of the air contained in the receiver, is 

 the more readily affected, as the animal placed under it is younger, more 

 robust, and his lungs are more capacious. Hence, birds, whose lungs are 

 very large, contaminate a considerable quantity of air, and consume more 

 quickly its respirable part. A frog, on the contrary, will remain a con- 

 siderable time, in the same quantity of air, without depriving it of 

 its oxygen. 



* See APPENDIX, Note W, 



