316 BOARD OF AGRICULTURE. 



animal life ; so, also, would one of pure nitrogen, which is a 

 gaseous body, having no affinit}" for animal tissues, like oxy- 

 gen, and is incapable of being absorbed in respiration, though 

 it is a constituent of all the tissues except the fatty, which 

 are chiefly carbon. It dilutes the oxygen, renders it respira- 

 ble, and modifies its destructive force. Carbonic acid is 

 essential to plant-growth, but, when it is present in air in a 

 high percentage, is speedily fatal to animal life by causing 

 spasm of the larynx and consequent asphyxia. In its pure 

 state it is irrespirable, and negatively poisonous. 



We find it mixed with the deadly carbonic oxide in deep 

 wells that have long been covered: and it has long been a 

 custom witli men Avho are about to descend into such wells 

 to first lower a lighted candle, and, if it would continue to 

 burn (showing the presence of oxygen), they would venture 

 to descend ; but this is no certain test that the air is safe, 

 and fit for respiration, for life may speedily become extinct 

 in an atmosphere in which a candle will continue to burn. 

 The only safe procedure is to force fresh air into the well 

 to displace the accumulated gases, before attempting to 

 descend. 



Carbonic-acid gas is pleasant and piquant to the taste, and 

 agreeably cordial to the stomach. 



Fuming champagne, sparkling cider, and the so-called 

 soda-fountain, owe their agreeable qualities to this gas. 



It is a product of the process of fermentation, is generated 

 in 3'east, is absorbed by the gluten of flour, which gives us, 

 when properly kneaded and baked, the light, porous, spongy, 

 well aerated bread of the skilful housewife. It issues from 

 th3 earth in the vicinity of volcanoes, and from fissures in 

 the rocks. It is generated in the bodies of men and animals 

 by the destructive metamorphosis of tissue, and tlie processes 

 of digestion, assimilation, and nutrition, and is excreted 

 chiefly by respiration. It is one of the chief products of 

 combustion, and is indispensable to vegetable growth. It is 

 found in high percentage in soils, in the air of close bed- 

 rooms, halls, schoolhouses, shops, and churches that are occu- 

 pied and poorly ventilated. 



Surrounded by climatic influences too severe for endurance, 

 we are obliged to enclose a small space or portion of air for 

 a habitation, to shelter, protect, and make us comfortable. 



