202 STABLES. 



to preserve the air inside the building at a standard of purity 

 which will be compatible with the preservation of the health 

 of the stabled animals. Although we have no means for 

 rigidly fixing that standard, which varies according to the 

 requirements of individual horses ; we may assume that 

 it is attained for all practical requirements when the air inside 

 the building is free from smell, and gives no sensation of 

 " closeness," or of warmth due to the presence of the horses. 

 Any fears on these points will be further allayed, if we find 

 that the place is roomy and lofty, and has free communication 

 with the outside air. 



Normal air contains from 0.02 to 0.06 per cent, of carbonic 

 acid. An excess of this gas causes distress, which is shown 

 by accelerated breathing, and diminution in the number 

 of the beats of the heart. Generally speaking, the breathing 

 of impure air induces diseases of the organs of breathing, 

 diminishes vitality, and favours the attack of infective diseases 

 when special bacteria are present. 



" Carbonic acid is not poisonous when taken into the 

 stomach, but acts most injuriously when breathed, by offering 

 an obstacle to the escape of carbonic acid gas, by diffusion, 

 from the blood of the venous circulation in the lungs, and its 

 consequent replacement by the oxygen necessary to arterial 

 blood. Any hindrance to this interchange must impede 

 respiration, and such hindrance would of course be afforded 

 by carbonic acid gas present in the air inhaled, in proportion 

 to its quantity. ... It may be safely asserted that it is 

 not advisable to breathe for any length of time in air contain- 

 ing more than yoVo-th ( ai P er cent.) of its volume of carbonic 

 acid gas. The air of a room contains too much carbonic acid 

 gas, if half a measured ounce of lime-water become turbid 

 when shaken in a half-pint bottle of the air " (Bloxam). 



The following are four ways by which ventilation can be 

 naturally obtained : 



