290 RESPIRATION. 



x 



with insufficient ventilation, the organic matter accumulates in the 

 atmosphere, and after a few hours its odor becomes exceedingly offen- 

 sive. According to Carpenter, if the fluid condensed from the expired 

 air be kept in a closed vessel at ordinary temperatures, a putrescent 

 odor is after a time exhaled, which could only come from some organic 

 substance in a state of decomposition. 



When perfectly fresh and in the healthy condition, the organic in- 

 gredient of the expired breath is not offensive and appears to have no 

 unwholesome qualities. It is only when accumulated in undue quantity, 

 and allowed to stagnate in the atmosphere, that its disagreeable properties 

 become manifest. It appears to be distinct in character for each species 

 of animal, and it is liable to be absorbed and retained for a time by any 

 porous material, as wood, rough plaster, or woven fabrics. It is easy 

 to distinguish by its odor the breath of cattle from that of sheep or 

 swine, and the odor remains perceptible in any small inclosure or trans- 

 portation-car in which these animals have been recently confined. The 

 organic ingredient of the expired air which communicates these quali- 

 ties to the breath has not been isolated in sufficient quantity to deter- 

 mine its exact composition. 



Vitiation of the Air by Continued Respiration. From what has pre- 

 ceded it is seen that the air, after being exhaled from the lungs, has 

 become altered in its constitution by diminution of its oxygen and the 

 addition of certain other materials derived from the breath. Under 

 ordinary conditions, this deteriorated air is at once diffused in the sur- 

 rounding atmosphere, rising to a higher level on account of its increased 

 temperature, and being readily dispersed by the aerial currents which 

 are always more or less in motion ; so that a fresh supply of air, with 

 its normal constitution, is taken into the lungs with each successive 

 inspiration. But when breathing is carried on in a confined space, the 

 air necessarily becomes vitiated ; and this effect is produced with rapidity 

 in proportion to the small extent of the air space and the number of 

 men or animals confined in it. 



This vitiation of the atmosphere by respiration is accordingly the 

 result of several different changes taking place at the same time, and its 

 effects are a combination of those due to all these alterations. 



So far as regards immediate danger to life, the diminution of oxygen 

 is no doubt the most important change in the vitiated air, when carried 

 to a sufficient extent. We have already seen that for man and the 

 mammalians, the air is completely irrespirable when its proportion of 

 oxygen is diminished to 10 per cent. In these experiments, however, 

 the carbonic acid exhaled was removed, as fast as produced, by the 

 action of an alkaline solution, so that the air was retained in a state of 

 purity except for its loss of oxygen. In the experiments of Leblanc, a 

 dog and a pigeon, breathing in a confined space, were both reduced to 

 extremities when the air still contained 16 per cent, of oxygen but was 

 also contaminated with 30 per cent, of carbonic acid. The different 



