THE HABITATION AND THE ATMOSPHERE. 173 



to a close atmosphere. It is generally agreed that this condition is 

 reached when the proportion of carbonic acid appi'oaches one thou- 

 sandth.* Observation shows, in fact, that the proportion of carbonic 

 acid increases in the same degree as the insalubrity of the air, and 

 may, up to a certain point, afford a measure of it ; but the inconven- 

 ience we suffer from bad air is in reality attributable rather to the 

 putrescible organic products of respiration and transpiration which it 

 contains. According to P6clet, the air driven out from the ventilating 

 chimneys of crowded rooms exhales an odor so noxious that it can not 

 be borne with safety, even for a short time. According to some chem- 

 ists, the disagreeable odor that characterizes close air is due to a partic- 

 ular substance possessing an alkaline reaction and the property of giv- 

 ing off ammonia, which escapes from the lungs.f The real culprits are 

 these miasms which affect the smell. The carbonic iacid, which is 

 comparatively an inoffensive gas, only indicates the change the air has 

 undergone. The experiments of MM. Regnault and Reizet go to 

 show that an animal can live in an atmosphere containing seven hun- 

 dredths of carbonic acid, provided the proportion of oxygen is main- 

 tained at twenty-one hundredths. Animals have been observed to 

 perish in a tight inclosure even when the carbonic acid is eliminated 

 as fast as it is formed, and the lost oxygen is restored ; and Mante- 

 gazza has shown that if two birds are placed under two different bell- 

 glasses, and the carbonic acid formed by one is absorbed by quicklime, 

 and the organic matter exhaled by the other is taken up by animal 

 charcoal, the latter bird will survive considerably longer than the 

 former. We add that Dr. Pettenkofer has been able to breathe for 

 several hours, without inconvenience, air containing one hundredth of 

 carbonic acid developed, not by respiration, but by a chemical process. 

 These facts indicate that the few thousandths of carbonic acid diffused 

 in it are not the cause of the effects produced by an atmosphere viti- 

 ated by respiration. The oxygen content diminishes in nearly the 

 same proportion as carbonic acid is developed ; but the effects pro- 

 duced by " close air " can not be explained by the deficiency — say of 

 one per cent — of oxygen ; that may be remedied in part by more ac- 

 tive breathing. 



Carbonic acid has sometimes been wrongfully charged with effects 

 which were really due to a small proportion of carbonic oxide, a prod- 

 uct of imperfect combustion and of the reduction of carbonic acid. 

 Carbonic oxide is a deadly poison, and destroys the red globules of the 

 blood. To its disengagement may be attributed the unhealthy effects 



* According to M. de Chaumont's observations in English barracks, the odor begins 

 to be perceptible when the proportion reaches 0*0008 ; and this hygienist is inclined to 

 reduce the admissible proportion to 0-0006 ; but I believe it sufficient to adopt one thou- 

 sandth as a limit which we shall be fortunate if we never exceed in practice. 



f It blackens sulphuric acid, discolors permanganate of potash, and communicates to 

 water in solution a fetid odor (A. Proust, " Trait6 d'Hygiiine "). 



