RESPIRATION. 121 



The new combinations cannot be in every part of the body, as Dr. 

 Stephens supposes ; for that combination will go on in the greatest 

 cold as well as in the greatest heat, and will produce the same heat in 

 both. If this were true, then we should never be cold. But we find 

 we may become so cold as that a part shall mortify. I do not imagine 

 that animal heat arises from putrefaction, or from actions at all of the 

 putrefactive kind; but from the chyliferous fermentation in the 

 stomach, the sanguiferous in the lungs, and [the molecular in] the vessels 

 in general in the body 1 . 



The heat of an animal cannot arise from respiration [alone] ; for no 

 animals respire so freely as fishes 2 : yet they generate veiy little heat, 

 but when called upon [as in a freezing mixture], and then their powers 

 of respiration must be very imperfect. 



On Respiration. 



Every part of an animal so exposed to the air as for the blood to be 

 affected by it in such manner as to support life, may be called Lungs, 

 or Respiratory Organ ; but what is commonly understood as such, is 

 an apparatus formed for that purpose, as a distinct part of the animal. 

 But I conceive it very probable that there are animals so simple in 

 their construction as not to require a peculiar structure for this purpose. 

 I even know there are many so constructed, where an apparatus of this 

 kind could not be applied, such an apparatus not according with the 

 other parts. Yet I do conceive that in such the application of air is 

 as necessary as in those where an apparatus is formed; but where 

 there is a distinct respiratory apparatus, there must be other corre- 

 sponding apparatuses. 



"VYhere there is such an apparatus, we find it admits of forms fitted for 

 the different modes of respiration ; yet all are included in the terms 

 Branchice, or Gills, and Pulraones, or Lungs. But there should be a 

 generic term, admitting of divisions into species, so as to be charac- 

 teristic of the orders of animals to which they belong. 



1 [In a bat the animal heat can be raised or depressed at pleasure, say from 50° 

 Fahr. to 65°, and inversely, merely by accelerating or retarding respiration : which 

 seems to show that where the whole' constitution is adapted for a high temperature, 

 combined with the facidty of losing it by torpidity, the animal heat may be gene- 

 rated by the respiratory independent of the digestive process ; but as circulation is 

 directly as respiration, the change of the blood in the capillaries may also assist.] 



2 [The visible movements of respiration in fishes are stronger and more frequent, in 

 reference to the denser medium to be moved, but the actual amount of respiratory 

 change is less than in the warm-blooded animals that breathe the air directly. A 

 truer view of the breathing of fishes is taken in the next paragraph.] 



