528 ' THE AIR AND LIFE. 



tissues themselves. The hiiiiis, notwithstaudiiiii- the opinion of physiolo- 

 gists of the last century and of Lavoisier liinisell", are but the inlet tlirough 

 which the vital gas is admitted. IJespiration is an operation essentially 

 chemical; the oxygen in air passes throngh tlie walls of the exceedingly 

 fiue capillaries of the lungs, wliere it finds in the red globules of blood a 

 certain substance, hemoglobin, which unites with it by virtue of its 

 chemical afllnity and transports it to every part of the organism, there 

 to assist in the chemical operations, especially the oxidations which 

 attend life iu the cells aud tissues or iu the organs formed by them. 

 The result is a production of carbonic acid, the oxygen of which is 

 supplied by the air and thecarbou by the tissues. Blood is then noth- 

 ing but a vehicle; it brings the re(|uisite oxygen to the tissues and 

 carries off the carbouic acid which would soou cause death, if allowed 

 to accunuilate there. 



While respiration is common to all animals, it is far from being 

 equally active in all; it is more intense in birds than in mammals, in 

 mammals than in reptiles and mollusks; ou the other hand, an active 

 animal will consume more oxygen than a slothful on(^ or one plunged iu 

 sleep, lethargy or hibernation. Yet all animals breathe; none can dis- 

 pense with oxygen, and if that gas fails them, they die. 



It is not otherwise with vegetables. True, plants exhale oxygen 

 through their function of nutrition, but, as was pointed out by Priestley, 

 they absorb some through their function of respiration. With them also 

 this function nuiy vary in intensity. During germination a large quau 

 tity of oxygen is required and we thus understand why so many seeds 

 can not germinate under water where the supply of oxygen is insuffi- 

 cient, or in compact soils that are not easily penetrated by air. One 

 seed may demand one-hundredth of its weight in oxygen, another seed 

 will thrive on one-thousandth or one-half of one-thousandth, but all 

 need some. Plants also require oxygen during growth; they consume 

 it in large quantities when blooming, at which time chemical operations 

 are so rapid and so intense as to give rise to (piite a perceptil)le produc- 

 tion of heat. At every instant in their lives they consume oxygen, and 

 it is for this reason that large quantities are not kept in our dwellings, 

 especially at night, when they produce carbonic acid, oxygen being 

 exhaled only by day. Even wheu api)arenMy dead, jilants still breathe; 

 their separated parts — blossoms, leaves, fruits — inclosed in a vase tilled 

 with air, consume oxygen and i)roduce carbonic acid. If i)la('ed in a 

 medium devoid of oxygen, death sjx'cdily follows. 



So then, no life is possible without oxygen, neither for animals nor 

 for plants. This much has been determined by science since the day 

 of Lavoisier's discovery. 



The hasty conclusion might be reached by some that an unusual pro- 

 portion of oxygen makes life more intense, and that wherever there is 

 a lack of air life is also absent. Investigations by Paul Bert, and 

 esj)ecially by M. Pasteur, during the last hfteen or twenty years, have 

 shown how erroneous are such conclusions. 



