AIR AND LIFE. 151 



are in direct contradiction with positive facts and observations we may 

 dismiss them as "■ children of fancy." The chemist Thenard analyzed 

 air collected at 7,000 meters height by Gay-Lussac, and found no trace 

 of such difference. Similar observations, due to Dumas and Boussin- 

 gault, prove that these theories are not sustained by stern reality, and, 

 in brief, chemists are agreed that, as far as oxygen and nitrogen are 

 concerned, the composition of atmospheric air is uniform and constant, 

 with very slight exceptions. This is the result of numerous observa- 

 tions made in different and distant places, at different heights, at dis- 

 tant epochs, and Dnmas and Boussingault, who have devoted much 

 work and time to the matter, have always obtained similar ratios, or at 

 least ratios so nearly identical that the differences are not more con- 

 siderable than may occur in the best-conducted experiments — they keep 

 within the limits of unavoidable errors. So we may consider air as 

 being as perfectly uniform in composition, as it might be expected to 

 be in Anew of the circumstances. 



Now, where did this oxygen originate? Whence does it come? From 

 what source is it supplied? A complete answer to this question can 

 only be given by those who know how things stood in the beginning, 

 and who understand the origin of matter, force, life, and some other of 

 those troublesome and perplexing problems. Oxygen must be a very 

 anciently established inhabitant of our planet, and its origin, like that 

 of the "old" families, is lost in obscure mystery. At all events there 

 it is, and wherever it comes from, howsoever it has been evolved, one 

 thing seems positive, and that is the fact that there are at present, 

 as far as we know, no important sources whence a considerable amount 

 of this gas may be derived and added to the current stock. In view 

 of this, the stability of its normal ratio in the air, notwithstanding the 

 enormous quantity of it consumed by living beings and in combustion, 

 becomes a riddle well worthy of some attention. 



We know that the entire atmosphere contains over one million billions 

 of kilograms of oxygen; that nearly one-half of the weight of the 

 minerals of our globe is oxygen; that eight-ninths of the weight of 

 water consists of this same gas, which is, moreover, abundantly present 

 in the tissues of all living organisms. On the other hand, we know 

 at present of but one source of oxygen, discovered by Priestley, and 

 further investigated by Perceval and Senebier. I refer to plants. It 

 is a fact familiar to all that plants are endowed with the faculty — 

 ascribed to the chlorophyll contained in their tissues 1 — of breaking up 

 carbon dioxide into its elements; that is to say, into carbon which goes 

 to the repair or increase of the tissues, and oxygen, which, on being 

 freed, diffuses itself throughout the surrounding atmosphere. There 

 certainly is one source of oxygen. Are there any others'? Their 

 existence is doubtful. Of course we know that a number of chemical 



'The (act is probable but not certain, for chlorophyll has not yet been satisfactorily 

 separated from the tissues in order to investigate its chemical powers. 



