78 HEALTH AND DISEASE 



(carbon dioxide), as well as various organic impurities or products of 

 decomposition given out with the expired air. How deadly these mixtures 

 of the products of respiration may become is illustrated by the con- 

 stantly-quoted case of the Black Hole of Calcutta, in which, out of 300 

 men who were imprisoned, 260 died very quickly from the poison which 

 they breathed from their own lungs. Carbon dioxide, which is one of the 

 products of combustion, is extremely poisonous, and contamination of the 

 air with more than 1 per cent is rapidly fatal to animals. Sulphuretted 

 hydrogen, a gas set free in the decomposition of organic matter, is highly 

 deleterious to animals. 



Ammoniacal vapours, which are constantly present in badly ventilated 

 stables, exercise an irritating effect on the sensitive membrane of the eyes, 

 and the comparative rarity in the present day of ophthalmia and other 

 serious diseases of the eyes among horses is ascribed to the improvement 

 which has taken place in the methods of construction and ventilation. 



Admixture of sewage gas with the atmosphere is probably responsible 

 for the occurrence of many forms of derangement of the digestive organs 

 which may often be attributed to other causes. 



Emanations from marshes were for a long time regarded as being the 

 immediate cause of certain specific fevers in man and animals, but while 

 marsh lands are undoubtedly unhealthy, it has now been demonstrated that 

 malaria is caused by inoculation with the germs of the disease through the 

 agency of mosquitoes. A somewhat similar case is that of the disease 

 following upon the bite of the tsetse fly in South Africa. 



The most dangerous forms of organic contamination are undoubtedly 

 the minute organisms, which under certain conditions produce specific 

 diseases when introduced into the bodies of animals, including man. The 

 different disease germs are active in different ways; thus, the germs of 

 phthisis (pulmonary consumption) may produce disease when inhaled; the 

 bacillus of enteric (typhoid) fever when swallowed; and the tetanus (lock- 

 jaw) bacillus when received into a wound or scratch. Pure air and water, 

 cleanliness and sunshine, are important weapons against these invisible foes. 



It may be observed that while air charged with disease germs may be 

 inhaled with impunity by the perfectly healthy animal, it may prove fatal 

 to the animal which is in bad condition. 



Cases of the injurious effects of contaminated atmosphere might easily 

 be multiplied, but enough evidence has already been advanced to prove 

 the necessity for a sufficient supply of pure air as one of the factors in 

 a condition of perfect health. 



Cubic Air-Space. — It has already been stated that each horse will 

 require something over 15,000 feet of pure air per hour, but this by no 



