HEREDITY— AIR 107 



oxygen 20.97 per cent, nitrogen 79 per cent, and carbon dioxid 

 gas (C0 2 ) .03 per cent. 



Impurities in air are taken care of by nature through dif- 

 fusion, oxidation, sunlight, and plant life activity. Common 

 impurities in air are carbonic gas, ammonia, and bacteria of 

 many different kinds; scales and debris of epithelium, hair, 

 sputum, dried manure, dried pus, etc. 



Relation to disease. — Diseases related to impure air are many 

 and serious. 



Horses' lungs have about 289 square feet of air-absorbing 

 surface or five times the skin area. They may contain at one 

 time 1.5 cubic feet of air. Horses at rest may give off 6.5 to 

 7.5 cubic feet of C0 2 every hour. 



Air begins to get foul when oxygen is reduced to 20.6 per 

 cent, or when C0 2 goes above .05 per cent; neither is neces- 

 sarily harmful, however. 



Carbon dioxid (C0 2 ) is not of itself poisonous in small quan- 

 tities but it is significant because of impurities with which it 

 may be associated. Common statements that C0 2 at 1 per cent 

 is very poisonous or fatal are nonsense. 1 "When present in very 

 great excess, it supplants oxygen, causes paralysis of heart, and 

 overwork, then failure of the lungs, and, finally, oxygen star- 

 vation. 



Hydrogen sulphide may also be present in the air. A very 

 small amount is said to be fatal to horses, causing diarrhea and 

 extreme weakness. 



Nitrogen is nearly negative in effect. It merely dilutes oxy- 

 gen and C0 2 . 



Ammonia in air must also be regarded as an impurity, so far 

 as animal life is concerned, mainly because of the organic mat- 

 ters with which it associates, and because of its irritating effect 

 upon the respiratory organs. 



Practical application. — A very practical lesson and a very 

 obvious one is breed from sound and vigorous stock. Farmers 

 who patronize unsound and inferior sires simply because the cost 

 of service is low are unwise. The Minnesota stallion law speci- 

 fies infectious diseases, and also the following diseases, as bars 

 for registration on the ground that they are transmissible either 

 directly or indirectly by heredity ; bone spavin, ringbone, side- 

 bone, and curb when accompanied by curby hock. 



'See Minn. Exp. Sta. Bulletin 98. 



