VENTILATION, AND THE REASONS FOR IT. 357 



the undefined impurity exists in large quantities, only rubbing can re- 

 move it rapidly, and this is done when we clean thoroughly walls and 

 furniture. If very bad, and time presses, while elegance is not a de- 

 mand, we cover the whole, and find whitewashing to be a ready mode. 



The other reasons for ventilating have arisen from scientific inqui- 

 ries. We wish to remove the carbonic acid ; we might be able to find 

 this gas by the senses, if it were very abundant ; but it, is not so as a 

 rule, until after our senses have informed us of the organic accompani- 

 ments. It furnishes, however, one of the most important and proba- 

 bly the most important of the reasons in every-day life, because car- 

 bonic acid is the most rapidly hurtful to animal life of all the emana 

 tions from the person. It lowers the vitality rapidly, and kills with 

 indefinite warning. The best warning is the organic matter, which 

 acts for both. The warning by carbonic acid is called indefinite, be- 

 cause people lose vitality, but do not observe that the cause is in the 

 atmosphere, there being no smell connected with that gas. At night, 

 when lights are burning, the carbonic acid warns better than the other 

 impurities, by simply putting out the candles. This seldom occurs in 

 private houses, but dim burning is common enough. Mr. James Na- 

 pier, F. C. S., tells me that he has seen the candles beginning to go out 

 in a small meeting-room in the country, which had a low ceiling and 

 was crowded. It was needful to keep the door open. How blunt, then, 

 is our perception of carbonic acid ! 



Another reason for ventilating is to remove solid floatino- bodies, 

 including infectious matter, fungi, and peculiar emanations arising from 

 disease or other anomalous conditions. These floating bodies can 

 sometimes be distinguished by the sense of smell in the case of mould, 

 for example. If it were possible to describe a smell completely, this 

 class would be largely subdivided, since experience has made many 

 persons very learned on this subject. It is, however, a knowledge 

 which we have not yet been able to receive from or communicate to 

 others. This whole question requires careful examination. The knowl- 

 edge of the smell cannot be taught, but it may guide us to much that 

 can be taught. Ventilation for this class of bodies will be probably 

 much more attended to in future ; care must be taken to drive them to 

 the nearest opening, and not to allow them to diffuse themselves 

 through the room in which they may be produced. In some cases re- 

 sort must probably be had to rapid artificial and heated currents. 



We ventilate to remove smoke and ordinary dust ; these are easily 

 seen ; and we use ventilation to procure dryness. Moisture rises con- 

 stantly from the skin, and, if an inhabited apartment is not ventilated, 

 that moisture accumulates. By opening the windows we cause floors 

 to dry sooner, and we remove moisture from all the apartments, and 

 that moisture has generally organic matter with it. If we ventilate 

 with very moist air, we shall dry nothing ; if we have very dry air, we 

 may dry too thoroughly. It is, however, better for us to have what is 



