24 THE COMPOSITION OF EXPIRED AIR, 



CONCLUSIONS. 



I. Tlie rosults oljtaiiu^<l in this research iudicate tliat in air exinreil by 

 healtliy mice, sparrows, rabbits, guinea-pigs, or men, there is no peculiar organic 

 matter wliich is poisonous to tlie animals mentioned (exchuling man), or which 

 tends to produce in these animals any special form of disease. The injurious 

 effects of such air observed appeared to be due entirely to the diminution of 

 oxyo-en, or the increase of carbonic acitl, or to a combination of these two factors. 

 They also make it very im[)rol)able that the minute quantity of organic matter 

 contained in the air exi)ired from human lungs has any deleterious influence upon 

 men who inhale it in ordiiiaiy rooms, and, hence, it is probably unnecessary to 

 take this factor into account in providing for the ventilation of such rooms. 



II. In ordinary (piiet re.xpiration, no bacteria, epithelial .scales, or particles of 

 dead tissue are contained in the expired air. In the act of coughing or sneezing, 

 such organisms or particles may prol)ably l)e thrown out. 



III. The minute quantity of ammonia, or of combined nitrogen, or other 

 oxidizable matters, found in the condensed moisture of human breath appears to 

 be largely due to products of the decomposition of organic matter which is 

 constantly going on in the mouth and pharynx. This is shown by the effects of 

 cleansing the mouth and tet-tli upon the amount of such matters in the condensed 

 moistui-e of the breath, and also by the differences in this respect between the air 

 exhaled through a tracheal fistula and that expii-ed in the usual way. 



IV. Tlie air in an inhabited room, such as the hospital ward in which 

 exi)eriments were made, is contaminated from many sources besides the expired 

 air of the occupants, and the most important of these contaminations are in the 

 form of minute particles or dusts. The experiments on the air of the hospital 

 ward, and with the moisture condensed therefrom, show that the greater part of 

 the ammonia in the air was probably connected with dust particles which could 

 be removed by a filtei-. They also showed that in this dust there were micro- 

 organisms, including some of the bacteria which produce inflammation and 

 sui>puration, and it is probable that these were the only really dangerous elements 



in this air. 



V. The experiments in which animals were compelled to breathe air vitiated 

 by the pioducts of either their own respiration or by those of other animals; or 

 were injected with fluid condensed from expired air, gave i-esults contrary to those, 

 reported by Hammond, by Bi-own-Suquard ;ui<l d'Ai-sonval, and by Merkel, but 

 corresponding to those reported by Dastre and Loye, RussoGiliberti and Alessi, 

 Ilofmann-Wellenhof, Rauer, and other experimenters i-eferred to in the pi-eliminary 

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



