THE HYGIENIC INFLUENCE OF PLANTS. 423 



transformation of matter in the body, which are regulated by the 

 requirements of breathing. The inhalation of oxygen is not a pri- 

 mary but a secondary thing. When we inhale air at every breath 

 richer than usual in oxygen for example, when breathing highly- 

 compressed air, as divers do, or laborers on the pneumatic founda- 

 tions of bridge-piers the result is not a larger consumption of matter 

 and an increased production of carbonic acid, but merely a decrease 

 in the number of inhalations. If in air of ordinary density we make 

 about sixteen respirations in a minute, in air of greater density we 

 should involuntarily make only twelve, ten, or eight, according to the 

 density and our need of oxygen; all else remains the same. 



Lavoisier, and, half a century later, Regnault and Reiset, placed 

 animals for twenty-four hours in air very rich in oxygen, but they did 

 not consume more of it than in the ordinary air. An increase of oxy- 

 gen in the air, therefore, or pure oxygen gas, only produces an effect 

 in certain mox-bid conditions, in cases of difficulty of breathing, or 

 where breathing has been for some time suspended, because an in- 

 spiration communicates more oxygen to the blood than breathing 

 ordinary air. A healthy person can, however, without difficulty or 

 injury, compensate for considerable differences, and an increase or 

 decrease of one or two per cent, of oxygen does no harm, for under 

 ordinary circumstances we only inhale one-fourth of the oxygen in 

 the air we breathe ; we inhale it with twenty-one per cent, and ex- 

 hale it with sixteen per cent. 



So far, therefore, as we feel ill or well in a winter garden, it does 

 not depend on the quantity of oxygen in the air, and there is no 

 greater appreciable quantity of oxygen in a wood of thick foliage 

 than in a desert or on the open sea. 



Let us also for a moment consider the ozone in the air, which may 

 be looked upon as polarized or agitated oxygen. After its discovery, 

 which has immortalized the name of Schonbein, was made known, it 

 was thought for a time that the key had been found for the appear- 

 ance and disappearance of various diseases, in the quantity of ozone 

 in the air. But one fact, which was observed from the first, shows 

 that it cannot be so ; for the presence of ozone can never be detected 

 in our dwellings, not even in the cleanest and best ventilated. Now, 

 as it is a fact -that we spend the greater part of our lives in our 

 houses, and are better than if we lived in the open air, the hygienic 

 value of ozone does not seem so very great. Added to this, the 

 medical men of Konigsberg long had several ozone-stations there, 

 during which time various diseases came and went, without, as appears 

 from the reports of Dr. Schiefferdecker, ozone having the slightest 

 connection with the appearance or disappearance of any of them. 



Dr. Wolf htlgel, assistant at the Hygienic Institute at Munich, has 

 lately been occupied with the question of the sanitary value of ozone, 

 but has arrived at only negative results. 



