36 TETEEINAEY HYGIENE 



It was during a dense fog of this description some years 

 ago, that such extraordinary mortality occurred among the 

 cattle at the Islington Show. 



Sulphurous acid is sometimes present to such an extent 

 in the air of cities, as to render the rain acid, and even 

 attack the softer kinds of stone used for building purposes ; 

 it also destroys vegetation. 



Coal-gas is a mixture of gases, principally hydrogen and 

 hydrocarbons. The most poisonous constituent is carbonic 

 oxide, of which between six and seven per cent, exists in well- 

 made gas ; one per cent, in the air of respiration may cause 

 death. A cubic foot of coal-gas yields about half a cubic 

 foot of carbonic acid ; an average burner used in a stable 

 burns five cubic feet of gas per hour, so the impurity in a 

 stable arising from gas combustion can easily be calculated. 

 One burner will impart to the atmosphere as much carbonic 

 acid as a horse. 



Impurities from Offensive Trades.* — ^These do not represent 

 such an important class in veterinary as in human hygiene, 

 for the reason that the presence of animals during the 

 process of offensive trades is seldom necessary. Still horses 

 are employed in mines, alkali works, copper - smelting 

 factories, etc., and to an extent exposed to the organic 

 vapours arising from glue-making, bone and blood boil- 

 ing, slaughter-houses and knackeries. 



The air in mines is generally saturated with moisture, 

 and contains an excess of carbonic acid, depending on its 

 depth; as much as '2 per cent, is found in deep mines, with 

 a reduction in the volume of oxygen. The temperature of 

 the ak is very uniform. 



Vitiation of the air of mines takes place by the respira- 

 tion of men and animals, gunpowder blasting, and the 

 evolution of carbonic acid and marsh gas from the strata 

 which are being worked. The atmosphere is full of dust, 

 yet miners suffer the least mortality compared with other 

 dust-inhaling occupations, and pit ponies, excluding acci- 



* Under the Pablic Health Act, 1875, no offensive trades can be 

 established without the consent of the local authorities. 



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