756 METABOLISM 



of asthma, and the reaction which some persons show when near to horses may be due 

 to anaphylaxis, but the symptoms are not at all like those of persons breathing polluted 

 air. 



Once and for all, the toxic theory, as we may call it, both in its new 

 and its old form, is disproved by a very simple series of experiments per- 

 formed a few years ago by Leonard Hill, Flack and others. 72 These ob- 

 servers kept rats and guinea pigs in deep boxes so that they were huddled 

 together in a very poorly ventilated place, the atmosphere of which indeed 

 often contained 1 per cent of C0 2 ten times more than the legal limit. 

 The animals lived and thrived for months, although they must have been 

 breathing air which was highly contaminated by the supposed volatile 

 proteins. Not only did the animals show no symptoms while in the box, 

 but they failed to exhibit any anaphylactic reaction when, after some 

 time, they were inoculated subcutaneously with the serum of animals of 

 the other species living with them in the box. This was really a most 

 excellent test of the anaphylactic theory because there are probably no 

 two animals in which anaphylaxis is more pronounced than in the rat 

 and guinea pig. The only things that were found to be of importance 

 in maintaining the animals in a thriving condition were cleanliness and 

 plenty of food. 



By an eliminative process we are gradually approaching the correct 

 solution of our problem, but before we proceed to consider this, it may 

 be well to remark that the odor of polluted air has nothing whatever to do 

 with its unhealthy influence, except in so far as it excites disgust and puts 

 one off his appetite. Indeed one very soon becomes so accustomed to these 

 odors that they fail entirely to be sensed after a short period in contact 

 with them. Their influence is entirely psychological. In many trades 

 and occupations people are constantly exposed to odors that are almost un- 

 bearable to one who is unused to them, and these people are perfectly heal- 

 thy, and indeed do not complain at all of the smells. 



We have so far considered in what is approximately their chronological 

 order the various hypotheses that have been brought forward to account 

 for the harmful influence of vitiated atmospheres. We have done this 

 mainly in order to correct any false conclusions that may still exist in 

 connection with the subject. 



And if further evidence be demanded to justify this position, there is 

 one crucial experiment which once and for all shows that changes in the 

 chemical composition of the atmosphere has no relationship whatsoever to 

 the unhealthful influence of vitiated air. This experiment is all the more 

 convincing because it was performed on healthy young men. In its simplest 

 form it consists in crowding as many persons as possible into an airtight 

 cabinet, provided with an electric fan, and with the necessary apparatus 

 for measurements of the physical and chemical conditions of the air. 



The following is a description of the results of such an experiment: 



