VENTILATION. 147 



pleasant odours are not always injurious, there can be no doubt 

 that constant exposure to the emanations of putrefaction, 

 especially such as is fed with meagre supplies of oxygen, 

 engendering products of unstable equilibrium, is thoroughly 

 baneful, and may exert its noxious influence with but little 

 warning given to the nostrils. 



All disinfectants in use act in one or other of two ways : 

 they either decompose organic matter, or they preserve or 

 pickle it; permanganate of potash, chlorine, and fumes of 

 burning sulphur being examples of the destructive kind, 

 while creosote and carbolic acid are instances of the pre- 

 servative or antiseptic description. 



111. Ventilation has for its object the preservation, within 

 buildings, of an atmosphere as free as possible from accumu- 

 lation of carbonic acid, or any other impurity, by affording 

 ingress to fresh air and egress to the vitiated. Practically, the 

 great problem is how to attain this end with as little admis- 

 sion of cold as possible, and without draughts. Draughts are 

 not only highly dangerous, ' on account of the well known, 

 but ill understood, sympathy between the secretion of 

 different parts of the integument and various internal organs, 

 but are deservedly regarded with much dislike, a dislike 

 which may be so great that impure air will be endured in 

 preference. To avoid draughts, the communication of a heated 

 room with the external air should be constant, free, and directed 

 away from the position of the inmates, or the air should be 

 heated by some special contrivance before it gains admission. 

 The dense air from without rushes into an apartment with the 

 greater force the narrower the aperture of entrance; and no 

 arrangement can well be imagined more likely to produce 

 exposure to draughts than a room with a warm fire on one 

 side, and insufficient ventilation taking place through the 

 key-holes and chinks of windows and doors on the other. 

 The heated air passes up the chimney, and cold air rushes in 

 streams with great velocity through the narrow apertures 

 opposite. The density of cold air gives it such force, in rush- 

 ing into a heated enclosure, that it travels inwards or falls 

 down through an opening in the ceiling very compactly ; 

 and, therefore, in good ventilation, means should be taken to 

 diffuse the entering streams of cold air, and direct them away 



