216 APPLIED PHYSIOLOGY 



produced by the air of different localities is to be attri- 

 buted ; yet upon such effects the undoubted benefits of 

 * change of air ' largely depend. Dalton even held the 

 view that chemical experiment could not distinguish the 

 air of Manchester from that of Helvellyn. This opinion, 

 though shared by other chemists, cannot any longer, 

 however, be regarded as accurate. Francis Jones,* for 

 example, found that on the same days, when the air in 

 the centre of Manchester contained on an average 

 4-526 parts of C0 2 in 10,000, that of Alexandra Park, 

 three miles distant, contained 3' 1186 parts, and when 

 the air of Manchester contained on an average 4'255 

 parts C0 2 , that of Arnside, near the Lake District, con- 

 tained only 3*237. Still, such comparatively small 

 differences as these can scarcely explain the difference 

 between town and country air. 



All that physiology clearly teaches on this subject, 



* * The Air of Eooms ' (Manchester : Taylor, Garnett, Evans 

 and Co.), 1900. Some of the results of Dr. Jones's experiments 

 may be summarized here : The air of a room always contains more 

 C0 2 than the external air, even when it is well ventilated. The 

 writer concludes that a certain amount of C0 2 is in some way 

 retained by the walls, and is constantly passing back into the room. 



The amount of C0 2 is always high during fogs and in snowy 

 weather, and is greater in winter than in summer. The air of a 

 room is always purest at the floor, less pure 3 feet above, and most 

 impure at the ceiling. 



When a coal fire is in use for heating and the electric light for 

 lighting an inhabited room, the air is purer than by any other 

 method of heating and lighting, and this is the only combination 

 which will keep the C0 2 in the air of the room below 10 parts 

 per 10,000. 



A room heated by a gas fire contains more C0 2 than one heated 

 by a coal fire. 



