RESPIRATION 197 



39. Nature's Provision for Purifying the Air. We have seen 

 that carbonic acid gas is heavier than air, and irrespirable. 

 Why, then, does it not sink upon and overwhelm mankind 

 with a silent, invisible wave of death? Among the gases 

 there is a more potent force than gravity, which forever pre- 

 vents such a tragedy. It is known as the diffusive power of 

 gases. It acts according to a definite law, and with a resist- 

 less energy compelling these gases, when in contact, to mingle 

 until they are thoroughly diffused. The added influence of 

 the winds is useful, by insuring more rapid changes in the air, 

 air in motion being perfectly wholesome. The rains also wash 

 the air. 



citadel. The leading cause of all this is, undoubtedly, the poor quality 

 of the food on which the lungs are nurtured. The very best physicians, 

 when their attention is directed to the subject, admit the full force of 

 this conclusion, and that it has not received the attention it deserves. 

 Professor Hartshorne remarks on this point, that 'the influence of 

 impure air in promoting consumption has probably heretofore been 

 underrated.' 'The vitiated air of the European barrack system for 

 soldiers,' says Professor Parkes, 'is the only way in which the great 

 prevalence of consumption in European armies can be accounted for.' 

 This is the conclusion to which the Sanitary Commissioners for the army 

 came, in their celebrated report : ' A great amount of phthisis (con- 

 sumption) has prevailed in the most varied stations of the army and in 

 the most beautiful climates in Gibraltar, Malta, Ionia, Jamaica, Trini- 

 dad, Bermuda, etc. in all of which places the only common condition 

 was the vitiated atmosphere which our barrack system everywhere pro- 

 duced. And, as if to clinch the argument, there has been of late years a 

 most decided decline in phthisis in these stations, while the only circum- 

 stance which has notably changed in the time has been the condition of 

 the air.' A very eminent authority, the late Dr. Marshall Hall, of Eng- 

 land, said, in reference to pure air in the treatment of consumption, ' If 

 I were seriously ill of consumption, I would live out doors day and 

 night, except in rainy weather, or midwinter ; then I would sleep in 

 an unplastered log house. Physic has no nutriment, gaspings for air 

 cannot cure you, monkey capers in a gymnasium cannot cure you, and 

 stimulants cannot cure you. What consumptives want is pure air, not 

 physic pure air, not medicated air plenty of meat and bread. ' Let 

 it be remembered, in this connection, that every hygienic or health-pro- 

 moting measure which tends to cure a disease is much more efficacious in 

 preventing it." Black's Ten Laws of Health. 



39. What can you state of the diffusive power of gases ? The added influence of the 

 winds ? 



