4 i 8 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



sity. For greater clearness we throw the explanation 

 into the form of several propositions. 



i. The Chemistry of Respiration.— The essential 

 chemical nature of respiration is an oxidation of food and 

 waste in the blood. Now, oxidation is a process of com- 

 bustion. Respiration is, therefore, a burning of food 

 and waste ; more specifically, it is a process of union of O 

 of the air with C and H of the blood, and the formation 

 of C0 2 and H 2 0, which are returned to the air. The 

 fouling of the air by respiration is due mainly to the 

 accumulation of the eliminated C0 2 . 



Proof. — The proof that oxygen is consumed and C0 2 

 eliminated in respiration is so familiar that it is unneces- 

 sary to give it except in bare outline, (a) Thrust a 

 lighted taper into a gallon jar, and it burns freely; but 

 blow into the jar through a tube reaching to the bottom 

 until the jar is filled with the expired air only, and again 

 introduce the taper; it is immediately extinguished. 



(b) Fill a test tube with clear limewater and blow through 

 the water with a glass tube for some time. The lime- 

 water becomes milky with precipitated lime, carbonate. 



(c) Take an equal bulk of pure air and of expired air 

 and compare their composition by analysis. It will be 

 found that in the expired air a certain volume of oxygen 

 has disappeared and been replaced by an equal or nearly 

 equal volume of C0 2 . So much for the C0 2 . Now for 

 the H 2 0. (d) Breathe on cold glass. Immediately the 

 clear glass is clouded with deposited water. 



Now, the union of oxygen with carbon and hydrogen 

 • — i. e., the combustion of carbon and hydrogen, always 

 produces heat. This, then, is the source of animal heat, and 

 the difference between warm-blooded and cold-blooded 

 animals is simply a difference in rate of combustion. In 

 warm-blooded animals, as birds and mammals, the whole 

 of the blood is oxidized, the surface of exposure is larger, 



