AMMAL HEAT. 



33. We are informed of the degree of alteration which the air 

 has undergone in our lungs, by the sensation which induces us to 

 renew it. This sensation, scarcely appreciable in ordinary respi- 

 ration, because we hasten to comply with the necessity of frequent- 

 ly renewing the air, becomes painful if not promptly satisfied ; and 

 is sometimes accompanied by anxiety, and even agony ; an in- 

 structive warning of the imperious necessity of respiration. 



34. In man there is commonly twenty inspirations per minute. 



35. In all the mammalia, in birds, and in reptiles, respiration 

 takes place in lungs, and very nearly in the same manner as in 

 man. 



36. In the greater number of aquatic animals, such as fishes, 

 lobsters, oysters, &c., it is altogether different, and respiration 

 takes place through the medium of a sort of membraneous frin- 

 ges called branch HE; we shall recur to this in the sequel. 



37. The air necessary to the support of life in insects, pene- 

 trates into all parts of their bodies through particular canals called 



38. Finally; there are some animals which have neither lungs 

 nor braiicliia-j nor truck a, in which respiration is accomplished 

 by the surface of the skin. The earth-worm is an example of this 

 kind. 



OF ANIMAL HF.AT. 



39. The greater number of animals appear cold when we 

 touch them, and indeed, the temperature of their bodies is not 

 much above that of the atmosphere, and changes with it. In 

 man, and other animals that approach him in their organization, 

 it is otherwise ; they have the faculty of producing a sufficient 

 quantity of caloric to maintain their temperatures, nearly always 

 at the same degree, under all atmospheric changes, and keep them- 

 selves warm. 



40. We designate under the name of cold blooded animah, all 

 those whose proper heat is not very perceivable, and call those 

 Wfinn l)lo(Hlt>tt uiiimuis which produce sufficient heat independently 

 of the atmosphere surrounding them. 



33 How are we made acquainted with the alteration the air has under- 

 gone in the lungs ? 



34. How many times does a man respire in a minute ? 



35. Does respiration take place in lungs in all animals ? 



36. In what organs docs respiration take place in aquatic animals? 



37. How does air enter the bodies of insects? 



38. How does respiration take place in those animals which have neither 

 lungs, nor branchiae, nor tracheae ? 



39. Are all animals of the same temperature? 



40. What is meant by cold blooded animals? What is meant bv warm 

 yl.oodeu animals? 



5 



