RESPIRATION. 425 



the lungs. It passes on with them, through the ar- 

 teries, into the minute capillary vessels which are 

 distributed throughout the body. In these vessels 

 their combination takes place, with the same produc- 

 tion of carbonic acid and evolution of heat, as if 

 the material were burnt in air or oxygen gas. The 

 carbonic acid thus formed is carried back to the lungs 

 in the venous blood, and there exhaled, through the 

 thin membrane of the air cells, and exchanged for a 

 new supply of oxygen gas. In view of the relations 

 of starch and sugar to the process of respiration, as 

 above shown, they have been termed the respiratory 

 constituents of the food. 



1057. RESPIRATION. In cold weather 



What is said . . 



further of res- a larger amount of oxygen is inhaled with 

 piratwn ? every breath, in consequence of the greater 

 density of the air. Respiration is also involuntarily 

 hastened, and the blood, from the two causes combined, 

 becomes more thoroughly impregnated with oxygen 

 gas. The transformation or combustion of the respi- 

 ratory constituents of the blood, proceeds more rap- 

 idly in consequence, and more internal heat is pro- 

 duced to oppose the external cold. This is one of the 

 provisions of nature by which the animal body is ena- 

 bled to resist the influence of the seasons and of cli- 

 mate. Labor has the same effect as cold in hastening 

 respiration and necessitating a larger supply of food. 



What change 1058. CHANGE IN COLOR OF THE BLOOD. 



of color does F rO m the fact that the globules of the 



the blood ex- 



perience in the blood undergo a change of color in the 

 lun s s - lungs, where oxygen is absorbed, it is pre- 



sumed that they serve, by absorption of the gas, as the 



