STABLES 



77 



ventilated, and the miners did not sutler from pulmonary affections, 

 excepting in an ordinary degree. The evidence of the extent to which 

 the air of mines is contaminated with coal-dust is of a very emphatic 

 kind. In the next illustration a specimen of a miner's lung is given, 

 showing the enormous accumulation of coal-dust in the lung structure. 



Stone-masons and metal-workers, also workmen in potteries, grinders, 

 button-makers, cotton-spinners, match-makers, and others have all been 

 mentioned as suffering from the effects of the contaminated air which 

 they habitually breathe. 



Horses are often looked upon as 

 animals which, to a great degree, 

 are exempt from the action of air con- 

 taminated in the manner described, 

 but the evidence in proof of this 

 belief is extremely meagre, in fact it 

 is mainly negative; indeed it does 

 not seem to have occurred to any- 

 body that the condition which we 

 have just illustrated of the coal- 

 miner's lung would be found in the 



A 



lungs of the horses working in the 



Fig. 4lifl. — Section from Upper Lobe of a Collier's Lung 



A, Deposits of coal dust in the air-vessels 

 (highly magnified). 



same pits if it were looked for, and 



there cannot be any doubt whatever 



that horses working in positions 



where the air is largely mixed with dust, or otherwise contaminated with 



mechanical impurities, would exhibit traces of injury from these causes 



in their pulmonary organs on post-mortem examination. 



Occasional outbreaks of disease have occurred among horses grazing 

 in the neighbourhood of brick-kilns and smelting-works, and chemical 

 investigation has demonstrated the existence of poisonous products in 

 the air which the animals had to breathe, and also in the pasture on 

 which they were feeding, and it is quite possible that in many instances 

 of unexplained outbreaks of affections of the respiratory organs the cause 

 might be found in the condition of the atmosphere, the presence in it of 

 either mechanical or chemical matters. 



Substances of a much more deleterious character than ordinary dust 

 undoubtedly obtain an entrance into the air; these come under the head of 

 organic impurities. 



Organic Impurities. — Contamination of the air constantly occurs, 

 and to some extent at least is inevitable ; the process of respiration, for 

 example, has the effect of charging the atmosphere with carbonic acid 



