166 AIR AND LIFE. 



iu all; it is more intense in birds than in mammals; more intense in 

 mammals than in reptiles and mollusks. An active animal will consume 

 more oxygen than one that is slothful, sleeping, lethargic, or hibernat- 

 ing. Yet all animals breathe; none can dispense with oxygen, and if 

 that gas fails them they die. 



It is the same with plants. While for their nutrition they exhale 

 oxygen (chlorophyllian function) during the day, under the influence 

 of light, they breathe at all times, absorbing oxygen and exhaling car- 

 bonic acid, as Priestley has shown. Here, also, the intensity of the 

 function may vary. Plants need a great amount of oxygen during 

 germination, and this explains why many seeds can not germinate 

 under water, where the access of oxygen is retarded and inadequate, or 

 in compact soil, where air — oxygen — is also deficient. One sort of seed 

 requires the hundredth of its weight iu oxygen, another is quite satis- 

 fied with ten or twenty times less; but all need oxygen, as De Saus- 

 sure proved nearly a century ago. 



Plants also need oxygen for their growth, and at the flowering period 

 they use a large amount of it, chemical operations being then so very 

 rapid and intense that a quite perceptible heat is given out. During 

 all moments of their life, from birth to death, plants breathe. Sepa- 

 rate parts, such as leaves, twigs, flowers, fruits, need and use oxygen 

 also — they are not dead; and a nosegay in a room plays its part in 

 the withdrawal of oxygen as well as the person sitting at the table, the 

 cat sleeping near the hearth, the lamps, the tire. A fruit or a leaf, 

 in any closed receiver full of air, alters the composition of the latter, 

 withdrawing oxygen and giving carbonic acid in its place. 



In brief, without oxygen there would be no life, no animals, no 

 plants; the whole planet would be one desolate landscape of rocks and 

 sand, from which the solar heat would in vain strive to elicit the merest 

 blade of grass, the smallest insect. 



Such being the case, some might incline toward the opinion that life 

 is abundant and intense in proportion to the amount of oxj'gen, while, 

 where air is deficient, life also is wanting. Logical extremes are, how- 

 ever, almost invariably absurd, and the researches conducted during the 

 last twenty years, by Paul Bert and Pasteur especially, go to show 

 conclusively that both opinions are equally erroneous. 



Living beings, as they are at present, are adapted to life in an atmos- 

 phere containing one-fourth oxygen and three-fourths nitrogen. Expe- 

 rience shows us that if the ratio of oxygen is decreased even by 

 one-fourth, life can no longer be maintained. The adaptation of organ- 

 isms to the atmosphere is thus very close, and this suggests the idea 

 that perhaps a change in reverse direction might also be injurious; 

 that an increase in the ratio of oxygen might prove- harmful. Paul Bert 

 has thrown much light on this question, and his experiments have 

 amply proven a fact which at first sight seems most improbable, but 

 is less surprising to those who always keep in mind the fact that living 



