ITS USES TO THE HUSBANDMAN. 241 



tains about 79 parts of nitrogen, 21 of oxygen, and near- 

 ly one of carbonic acid. A greater or less quantity of 

 oxygen unfits it for healthy respiration, and causes disor- 

 ganization and disease in the animal system. When at- 

 mospheric air is inhaled upon the lungs, it parts with 8 

 or 8^ per cent, of its oxygen, and receives in return a 

 like quantity of carbonic acid. Thus atmospheric air 

 becomes rapidly vitiated by being breathed, and is as 

 speedily restored to its purity by healthy vegetation, which 

 takes up the carbonic acid, or decomposes it, and gives 

 off, or sets free, oxygen. According to Dr. Bostock's 

 estimate, an average-sized man consumes about 45,000 

 cubic inches of oxygen, and gives out about 40,000 of 

 carbonic acid, in 24 hours. " Taking," says Dr. Combe, 

 '' the consumption of air at 20 cubic inches at each breath- 

 ing, as a very low medium, and rating the number of res- 

 pirations at 15 in a minute, it appears that, in the space 

 of one minute, no less than 300 cubic inches of air are 

 required for the respiration of a single person. In the 

 same space of time, 24 cubic inches of oxygen disappear, 

 and are replaced by an equal amount of carbonic acid, so 

 that in the course of an hour one pair of lungs will, at a 

 low estimate, vitiate the air by the abstraction of no less 

 than 1,440 cubic inches of oxygen, and the addition of 

 an equal number of carbonic acid, thus constituting a 

 source of impurity which cannot with safety be over- 

 looked." 



Atmospheric air becomes vitiated by one, or a combi- 

 nation, of the following causes : — 



1. By animal respiration ; 



2. By decaying animal and vegetable matters ; 



3. By stagnant waters ; and, 



4. By combustion in close apartments. 



Many cases are cited of the fatal effects of breathing 

 highly-vhiated air in prisons, in small, close apartments, 

 and in unhealthy districts. One of the most horrible was 

 that which occurred in the Black Hole of Calcutta, where 

 one hundred and forty Englishmen were thrust into a 

 confined place, eighteen feet square, in which there were 

 but two small windows on one side, and where ventilation 

 21 XV. 



