THE PHYSIOLOGICAL PRINCIPLES OP VENTILATION 755 



now well-known fact that a certain amount of this gas in the alveoli is absolutely es- 

 sential to the well-being of the animal, the whole hypothesis of its toxic action becomes, 

 to say the least of it, absurd. Indeed so important is the presence of this constant 

 amount of CO 2 in the alveolar air that whenever there comes to be a marked increase in 

 the amount of CO 2 in the atmosphere, the breathing becomes greater, so as to ventilate 

 the air sacs more thoroughly, and thus keep the relative amount of CO 2 in them at the 

 normal level. The extent of this increase in respiration is usually so small as to be 

 unnoticed by the individual, and certainly increased breathing is not one of the symp- 

 toms of which persons complain who are living in polluted atmospheres. 



In the face of such evidence, even the most ardent supporters of the 

 theory that the vitiated air owes its evil influence to C0 2 , were compelled 

 to abandon their position, but they did not do so without a final attempt to 

 retain for determinations of C0 2 a certain significance in the appraisement 

 of the healthfulness of air. Their new interpretation was to the effect that 

 the C0 2 percentage is proportional to the amount of deleterious organic 

 matter, and for many years this view prevailed. It is still believed by some 

 that an increase from the normal of 3 to 10 parts of C0 2 per 10,000 parts 

 of air indicates a degree of organic pollution which is dangerous to health. 

 More recent work definitely shows, however, that this view also must be 

 abandoned, and there remains for C0 2 -analysis only the secondary value 

 that it indicates, in a readily measurable way, to what extent the inside air 

 is being mixed by ventilation with pure air from the outside. However 

 free this dilution may be, the atmosphere may still be deleterious to health 

 and comfort unless certain other properties of it are incidentally altered. 



This interpretation of the value of CO, analysis naturally leads to a con- 

 sideration of the next possibility, namely, that the air in confined spaces 

 is contaminated by the accumulation of organic poisons derived from the 

 exhaled air of the persons living in it. 



It is many years ago now since experiments apparently proving this hypothesis were 

 published. These have been shown to be entirely fallacious, and we need refer to only 

 one group of them here, namely, those that were devised to show that inhalation by one 

 animal of volatile proteins contained in the exhaled air of others caused anaphylactic 

 reactions (page 90). As proof for this hypothesis, experiments were performed in 

 which a man breathed through a filter of glass wool (to catch any saliva) into a cooled 

 vessel, and the condensed vapor was then inoculated in appropriate dosage into guinea 

 pigs, so as to sensitize them, and a month or so later the animals were inoculated with a 

 minute trace of human blood serum. The injected animal showed decided symptoms of 

 anaphylactic shock, whereas other animals not previously sensitized were unaffected by 

 the injection of the same amount of serum. Such results taken by themselves did seem 

 to afford substantial support for the new hypothesis, but it is almost certain that they 

 depended on contamination of the condensed vapor by traces of saliva which it is im- 

 possible to keep out by any kind of filter. This saliva contains traces of soluble protein 

 (mucin) wh'ch had been responsible for the anaphylactic reaction. The symptoms are, 

 however, entirely dissimilar from those of a vitiated atmosphere. Hay fever, some forms 



