CHEMISTRY OF RESPIRATION. 379 



a man can breathe without difficulty if there are but 15 volumes per 

 cent. So far, then, as the question of oxygen is concerned, a man 

 could breathe where a candle would not -burn, but it does not 

 necessarily follow that it is always safe for a man to venture where 

 a candle will burn, for sometimes, although there may be oxygen 

 sufficient to sustain life, poisonous gases may also be present in an 

 amount sufficient to produce a fatal result. It would be a surer 

 test to place a dog in the suspected place and leave him there for 

 twenty minutes. If it survives, it will be safe for a man to enter. 



It is a matter of common experience that injury to health 

 follows confinement in badly ventilated apartments, but the cause 

 thereof has never been satisfactorily determined. The generally 

 accepted theory is that it is not due to the carbon dioxid which is 

 given oif by the lungs, but to the organic matter crowd-poison 

 exhaled in the expired air and also given off from the surface of 

 the body, especially of those who are not cleanly in their habits, 

 and who resort to bathing the body too infrequently. Those who 

 maintain these views state that an air which contains respiratory 

 CO 2 i. e.j CO 2 produced by respiration to the amount of more 

 than 0.07 per cent, is unwholesome air to breathe, and yet that 

 CO 2 may be present to the extent of 2 per cent, provided that its 

 presence is due to 'chemical processes, as in soda-water factories, 

 and may be breathed without inconvenience or any injurious conse- 

 quences resulting. Indeed, so reliable observers as Brown^S^quacd 

 and (PArsony^l have breathed air in which CO 2 was present to the 

 amount of 20 per cent, for two hours without marked distress. 

 When, therefore, injurious effects follow from breathing air con- 

 taining 0.8 per cent, of CO 2 , which represents that present in a 

 very badly ventilated lecture-hall, it must be due to something 

 else than the CO 2 , and they attribute it to the organic matter 

 already referred to. Brown^Se^iiard and d'Arsonval, who believed 

 that it was the organic matter from the lungs wKTch was the poison- 

 ous matter, injected into rabbits the condensed vapor of the ex- 

 pired air with fatal results. 



On the other side of the question are those who maintain that 

 the injurious consequences of breathing vitiated air are due to the 

 excessive amount of CO 2 and the deficiency of oxygen, and not to 

 organic matter. In support of this theory we have the following 

 observations : Haldane and Lorraine Smith found that in breathing 

 air containing 18.6 per cent, of CO 2 , within a minute or two they 

 suffered from hyperpnea, distress, flushing, cyanosis, and mental 

 confusion ; and the injections of condensed vapor-breath into 

 rabbits, practised by Brown-Sequard and d f Arson val, have been 

 repeated by several experimenters with negative results. Besides 

 these, other experiments have been performed, showing that no 

 volatile poisons are exhaled with the expired air. Among recent 

 investigations on this subject are those of Haldane and Lorraine 

 Smith. From these they conclude as follows : 



