46 STABLE ECONOMY. 



The Object of Ventilation is to procure a constant supply 

 of air in sufficient purity to "meet the demands of the animal 

 economy. Sufficient purity is not perfect purity. Neither 

 the horse nor any other animal requires air absolutely pure. 

 In towns and in stables there is no such thing ; and that is 

 proof strong enough that it is not essential. 



The Composition of Pure Air has been repeatedly ascer- 

 tained by chemical research. The atmosphere consists of 

 two simple gases. According to Lavoisier, 100 measures of 

 ■pure air contain 73 of nitrogen and 27 of oxygen. [Accord- 

 ing to later authorities, within a fraction of 21 of oxygen and 

 79 of nitrogen, and about 25V0 °f carbonic acid.] It has 

 been proved that a breathing animal consumes the oxygen, 

 and that death ensues when the supply falls below the de- 

 mand. When a small animal is enclosed in an air-tight ves- 

 sel, it soon dies. The air suffers no apparent diminution in 

 bulk, yet it undergoes a change in composition. The oxygen 

 is consumed, or a large portion of it is consumed, and its 

 place is occupied by another gas, termed carbonic acid, which 

 is given out from the lungs. This kind of air is rather 

 heavier than that of which the atmosphere is composed. In 

 certain situations it mingles with the air in the proportion 

 of about 1 to 100. When an animal is completely immersed 

 in it, he dies immediately. Some contend that carbonic acid 

 is poisonous ; others that it destroys life merely by excluding 

 the common air, without which no breathing animal can live. 

 The carbonic acid is an evacuation ; it exists in the system, 

 but it must not accumulate there. It must be throwi? out 

 almost as rapidly as it is formed. As it is evacuated, it con- 

 taminates the external air with which it mingles. Hence, in 

 the neighborhood of all animals, the air is more or less im- 

 pure. 



The Use of Air , in the animal economy, is to purify the 

 blood. This fluid is in a state of constant change. As it 

 circulates through the various parts of the body, it performs 

 functions innumerable ; these operations change its composi- 

 tion, and render it unfit to repeat them unless it be duly 

 renovated. In the lungs the air and the blood come in con- 

 tact, and both are changed. The air loses a certain portion 

 of oxygen and acquires carbon. It becomes of a brightei 

 red; from a dark purple hue it is changed to bright scarlet. 

 The process is briefly described by the word purification. 

 But it must be remembered that, besides parting with some 

 noxious ingredient, the blood is altered in some other way 



