408 THE COMPOSITION OP EXPIRED AIR. 



organic matter which is constantly going on in the month and pharynx. 

 This is shown by the effects of cleansing the mouth and teeth upon the 

 amount of such matters in the condensed moisture of the breath and 

 also by the differences in this respect between the air exhaled through 

 a tracheal fistula and that expired in the usual way. 



4. The air in an inhabited room, such as the hospital ward in which 

 experiments were made, is contaminated from many sources besides the 

 expired air of the occupants, and the most important of these contam- 

 inations are in the form of minute particles or dusts. The experiments 

 on the air of the hospital ward and with the moisture condensed there- 

 from show that the greater part of the ammonia in the air was proba- 

 bly connected with dust particles which could be removed by a filter. 

 They also showed that in this dust there were microorganisms, includ- 

 ing some of the bacteria which produce inflammation and suppuration, 

 and it is probable that these were the only really dangerous elements 

 in this air. 



5. The experiments in which animals were compelled to breathe air 

 vitiated by the products of either their own respiration or by those of 

 other animals, or were injected with fluid condensed from expired air, 

 gave results contrary to those reported by Hammond, by Brown- 

 Sequard and d'Arsonval, and by Merkel, but corresponding to those 

 reported by Dastre and Loye, Russo-Giliberti and Alessi, Hofmann- 

 W ell en h of, Rauer, and other experimenters referred to in the prelim- 

 inary historical sketch of this report, and make it improbable that there 

 is any peculiar volatile poisonous matter in the air expired by healthy 

 men and animals other than carbonic acid. It must be borne in mind, 

 however, that the results of such experiments upon animals as are 

 referred to in this report may be applicable only in part to human 

 beings. It does not necessarily follow that a man would not be injured 

 by continually living in an atmosphere containing 2 parts per 1,000 of 

 carbonic acid and other products of respiration, of cutaneous excretion, 

 and of putrefactive decomposition of organic matters, because it is 

 found that a mouse, a guinea pig, or a rabbit seems to suffer no ill 

 effects from living under such conditions for several days, weeks, or 

 months, but it does follow that the evidence which has heretofore been 

 supposed to demonstrate the evil effects of bad ventilation upon human 

 health should be carefully scrutinized. 



6. The effects of reduction of oxygen and increase of carbonic acid to 

 a certain degree appear to be the same in artificial mixtures of these 

 gases as in air in which the change of proportion of these gases has 

 been produced by respiration. 



7. The effect of habit, which may enable an animal to live in an 

 atmosphere in which, by gradual change, the proportion of oxygen has 

 become so low and that of the carbonic acid so high that a similar 

 animal brought from fresh air into it dies almost immediately, has been 

 observed before, but we are not aware that a continuance of this 



