3 i8 THE POPULAR SCIENCE MONTHLY 



Perhaps the last word has not yet been said on this subject ; never- 

 theless I strongly suspect that ozone does not deserve the reputation 

 which commercial interests are endeavoring to foist upon it and that 

 as a panacea it is destined to follow into oblivion phylacteries and 

 amulets, blue glass and the rabbit's foot. 



Carbon dioxide within man's body performs certain useful purposes. 

 Generated in all of his tissues and passed from his cells into the lymph 

 and blood that bathe them, when in not too large quantity it reacts upon 

 the tissues as a hormone, or excitant, to stimulate them to greater ac- 

 tivity. It thus for a time, during the earlier stages of a task and be- 

 fore fatigue sets in, augments our working power. One of its most 

 striking services is that of acting as the stimulus to that part of our 

 nervous systems which presides over our respiratory movements. After 

 each expiratory act the accumulating carbon dioxide within our blood 

 excites our respiratory center to a subsequent inspiration, and except 

 for this substance within us respiration would be impossible. But when 

 in larger quantity than is required for these needs carbon dioxide is 

 poisonous to our tissues, causing fatigue and depression of working 

 power, and for the good of the organism must be expelled. It is, there- 

 fore, carried to the lungs and passed into the air. Thus much of the 

 carbon dioxide of the atmosphere represents a waste and poisonous 

 product of protoplasmic activities, of no use to man, however valuable 

 it is to the green plants. When breathed in excessive quantity it may 

 cause a feeling of suffocation, headache, nausea and other unpleasant 

 sensations, and may ultimately even be fatal. But the poisonous prop- 

 erties of carbon dioxide have been exaggerated. Thus while normally 

 it is present in free air in only about three hundredths of one per cent., 

 the breathing for hours of more than thirty times this amount does not 

 appear to be detrimental to the individual. In fact it has recently been 

 shown by Crowder that the air immediately before our faces is con- 

 taminated with expired carbon dioxide in varying quantities which in 

 extreme cases may reach one per cent. Except where ventilation is 

 very vigorous, as in facing the breeze of an electric fan, we are thus 

 habitually rebreathing a portion of the air which has previously en- 

 tered our lungs. In the face of such facts the minute variations of car- 

 bon dioxide in unconfined air are altogether negligible from the hygienic 

 standpoint. Thus the proportion of this gas is greater in the air of 

 cities than of the country, in night air than in that of day, in fogs than 

 in clear weather, with a low than with a high barometer, at the foot 

 than on the tops of mountains, and inland than at the seaside. But all 

 such differences amount to merely a few thousandths of one per cent, 

 and are probably of no importance whatever in the life of the individ- 

 ual. There is a larger proportion of the gas in the more or less con- 

 fined air of crowded assemblies, school rooms and industrial work 



