85 CAUSES AND PREVENTION OF DISEASE. 



AIR. 



Air is a very frequent source of disease. Composition in a 

 general way: — oxygen 1-5, nitrogen 4-5; more accurately, oxygen 

 20.97%, nitrogen 79.% and CO2, .03%. 



Impurities in air are either organic or inorganic. They are 

 taken care of by nature through dilfusion, oxidation, sunlight, 

 and plant life activity. 



Organic impurities in air are germs of several hundred dif- 

 ferent kinds ; scales and debris of epithelium, hair, sputum, dried 

 manure, dried pus, and various matters from sewer pipes and 

 marshy grounds. 



Inorganic impurities are abundant ; e. g., bits of various solid 

 particles which may travel great distances. 



E-elation to disease. — Diseases related to impure air are 

 many and serious ; e. g., total mortality among French cavalry 

 horses was formerly as high as 18% to 20%, but reduced by ven- 

 tilation and better sanitary conditions to 7%. Farcy in the Eng- 

 lish cavalry used to be exceedingly common, but is now rare. In 

 1857 there was a serious outbreak of influenza that could not be 

 checked until certain stables were cleaned and ventilated. 



Horses' lungs have 289 feet of air absorbing surface or five 

 times the skin area. They may contain at one time 1.5 feet of 

 air. Horses at rest may give off 6.5 to 7.5 cubic feet of CO2 

 every hour. 



Air begins to get foul and dangerous when oxygen is reduced 

 to 20.6%, or taking another moans of estimating, air begins to be 

 foul when CO2 goes above .05%. 



Carbon dioxide is most abundant close to the ground, be- 

 cause heavy. It is not very poisonous in small quantities of itself, 

 but serious because of the poisonous inorganic impurities with 

 which it is associated. It is rapidly fatal when it constitutes 

 more than one per cent, of total air. Its effects on animals, 

 when in excess, are: decrease of arterial pressure, supplants oxy- 

 gen inM^lood, causes paralysis of heart, and causes overwork, then 

 failure of the lungs. 



Hydrogen sulpliidc may also be present in tlie air. Four 

 per cent, is fatal to horses. It causes diarrhoea and extreme 

 weakness. 



