RESPIRATION 301 



appreciable. Russell found, for example, that in London the per- 

 centage of CO 2 might rise to 0.14 during a dense fog. 



Along with CO 2 there are present in the air of towns a number 

 of other impurities. From fires a good deal of unburnt CO passes 

 off. In the air of the underground railways when steam loco- 

 motives were still used, I found that about I volume of CO was 

 present for every 12 volumes of CO 2 . If we assume the same pro- 

 portion for the air of a town, there would be about .01 per cent 

 of CO present in the air of a bad London fog. This would be 

 sufficient in time to saturate the haemoglobin with CO to the ex- 

 tent of about 17 per cent, and might thus produce appreciable 

 effects on persons already in bad health, though healthy persons 

 would not notice any effect. 



Much more appreciable, however, are the effects of the par- 

 ticulate impurities. Ordinary coal contains a good deal of sul- 

 phur; and the sulphur, in the process of combustion, is mainly 

 oxidized to sulphuric acid, which condenses along with water 

 in the form of minute droplets and thus helps to form fog. Of the 

 unpleasant irritant effects of this sulphuric acid one can form a 

 good idea in passing through a railway tunnel, particularly if the 

 train is moving slowly up an incline and the coal burnt contains 

 much sulphur. Those familiar with sulphuric acid fumes in chemi- 

 cal laboratories or factories will at once recognize them in the 

 tunnel air. When badly purified lighting gas is burnt in a room, 

 the same irritant effect is also noticeable to a less degree. In a bad 

 fog in a large town the choking effects of sulphuric acid con- 

 tribute largely to the unpleasant effect of the fog and the manner 

 in which the fogginess of the air persists even when the air is 

 warmed in the interior of a house. There is no escape from this 

 effect unless the air is scrubbed or filtered. The sulphuric acid is 

 also destructive to metal and other materials. 



Besides sulphuric acid the smoky air contains particles of black 

 carbonaceous matter which greatly help absorb the light, and 

 also contains substances which have an unpleasant odor and more 

 or less irritant effect on the air passages. As will be shown below, 

 there is no reason to believe that the continued inhalation of these 

 particles has any deleterious effect on the lungs, and in ordinary 

 town air they are not present in sufficient concentration to be of 

 any direct consequence in other ways to health. Their greatest 

 importance arises from the inconvenience and expense caused by 

 their obstruction of light and the manner in which they dirty 

 clothes, walls, ceilings, and everything else in a house. By the 



