THE HORSE ANA TOM Y A ND PH YSIOLOG Y. G 1 7 



Physiology of Respiration. The chief end of respira- 

 tion or breathing seems to be the absorption of oxygen from 

 the air, and the elimination of carbonic acid from the blood. 

 Respiration is slower when the animal is in a state of rest than 

 when in motion. Carbonic acid is constantly developed in the 

 system by the decay of tissues, and by the conversion of car- 

 bon of the food which is used for the development of heat. 

 The vigorous exercise of force augments the destruction of tis- 

 sues, hence, the necessity of more rapid and deep breathing 

 while the animal exerts power, that oxygen may be more freely 

 supplied to, and carbon carried from, the blood. Here we see 

 the wisdom of nature in providing the racer with such superior 

 nostrils and lungs, and also an enlarged system of blood vessels, 

 that so display themselves under the fine skin of the racer on 

 the course. As the venous blood is brought into contact with 

 the oxygen through the thin membranous lining of the lungs, 

 we see the terrible tax placed on this organ by intense and long- 

 continued exertion. Here arises the danger often incurred of pro- 

 ducing rupture of these delicate lung cells and membranes, caus- 

 ing injury to the wind of the horse. From serious injury, 

 whether caused by over-exertion or long exertion in extremes 

 of heat or cold, inflaming the lungs, we have wind impaired 

 and dangerous lung fevers. 



Under favorable circumstances the blood enters the lungs, 

 and is acted on by the atmospheric air, absorbing oxygen, while 

 giving off volumes of carbonic acid gas. In passing through 

 the small blood vessels, the arterial blood loses about eight per 

 cent of oxygen, and receives about nine per cent of carbonic acid 

 gas; and when the blood is exposed to the action of atmospheric 

 air in the lungs, it receives oxygen and loses carbonic acid gas. 

 By this the blood changes color from a dark red to a bright 

 scarlet, or pure blood. 



Physiology of Digestion. For the descriptive anatomy 

 of the stomach and digestive apparatus, we must refer the reader 

 to larger works on anatomy. We must be content with a glance 

 at the physiology of digestion, that we may better understand 

 the care and feeding of our domestic animals and ourselves. 



