29 
ammonia in small quantities, are from much the same source as the 
carbonic acid. Our breath contains comparatively large quantities. 
Air fouled by the gases produced by decay, by sewage emanations, by 
contact with fifth of all kinds, is loaded with organic matter, largely in 
the form of noxious gases, which may contain disease germs, but which, 
at all events, is extremely detrimental to health. 
The unpleasant odour, and sometimes even taste, experienced on 
entering crowded and heated rooms, is due to organic matter in the 
atmosphere. The pleasurable sense of relief on going out into the 
fresh air from a room, is a sure indication that its air is seriously con- 
taminated with organic matter. We should take care that we do not 
habituate ourselves to unpleasant odours of this kind. The constant 
smell of food in the house should be avoided, or rather prevented. 
Dust should not be allowed to accumulate in carpets ; worn clothing 
should be thoroughly aired before putting away, and above all, defec- 
tive drainage should at once be made perfect 
AIR VITIATED BY RESPIRATION. 
Let us now briefly recapitulate those points, in which expired air 
differs from that of the atmosphere. 
i. Its oxygen is largely reduced. By respiration between 4.5% 
and 5.0% of oxygen is removed for the combustion of the food material 
in the blood. 
2. It contains a considerable amount of organic matter of a par- 
ticularly deleterious character. From the lungs alone about 3 grains are 
thrown off daily, and to this must be added the variable amount from 
the exhalations of the skin. 
3. The carbonic acid is largely increased. While fresh air contains 
about 4 volumes of carbonic acid per 1 0,00c, expired air contains 
between 400 and 450 volumes in the same quantity. This tremendous 
increase is easily understood when we remember that the individual 
breathes about 18 times per minute, and at each respiration produces 
nearly 1 yk cubic inches of carbonic acid. This amounts to yi cubic 
feet per hour, or at least 16 cubic feet in the 24 hours a quantity 
equal to that produced by the burning of 7^ oz. to 8 oz. of carbon. 
4. The amount of aqueous vapor is augmented, for, as we have 
