and ammonia; but I shall show that this is not the case. Oxygen alone remains in relatively larger and larger proportions; it has increased since the first living beings appeared, and its present maximum coincides with the maximum development of the central nervous and brain tissue of the animal world. As for carbonic acid, for the last half century chemists have noted it as only 6, 5, and 4 parts on 10,000 parts (volumes) of air. The latest determinations by Reiset (a very careful chemist, pupil of Boussingault, and one of the editors of Millon's well-known Annuaire), made at a country place, many miles from Paris, gave only 3 volumes of carbonic acid on 10,000 volumes of air in 1889, and he could not get a fraction more. Pelouze, master of the Mint at Paris, who was one of the most expert chemists of modern times, held the opinion that the atmosphere might be undergoing very slight variations which will only become appreciable to analysis after a great number of years. Baudrimont, and other eminent chemists have held similar views, admitting that the socalled fixity of composition is only apparent, not real. CHAPTER II. Respiration in the Lowest Forms of Life-Eremacausis ANATOMY and physiology cannot teach us how respiration is effected in the lowest creatures in the scale of life, those which are supposed to have been the first produced. All vestiges of a respiratory organ are absent, unless it be the cell wall or outer envelope that breathes. Until my recent experiments were made (which, however, were preceded in another direction by those of Pasteur, when he discovered the anaerobic ferments), no one could say whether these beings require free oxygen or not; though this could be proved for higher organisms, such as fish and tadpoles, which live in water. I found that the microscopic unicellular algæ, Protococcus pluvialis, P. palustris, etc., carry on their respiratory functions much as the higher organized plants do, but with more energy. In such animals as Holothuria tubulosa, the functions of respiration is little, if at all, separated from that of the intestine: water is sucked in, three times a minute, and remains about. twenty seconds in the animal's body. It is not yet known with certainty whether these lower forms of life may be able to derive oxygen from water, or carbonic acid, or both. But it is evident that oxygen is essential both for plants and animals, however low in the scale; in fact, that oxygen and life seem to be synonymous terms in this respect; only, we must distinguish between oxygen in combination, and the free oxygen of the atmosphere. Koene's ingenious theory to which I have alluded is based upon the incomplete eremacausis of organic matter which is confided to the earth, and protected from the action of the air, by which means enormous quantities of carbon have always been, and are still being, slowly subtracted from the atmosphere. He did not believe that this element can be supplied from without-from cosmic space and it thus disappears for ever from our atmosphere. But is this eremacausis, or slow combustion, really so incomplete? Is not carbonic acid returning in immense quantities to the atmosphere, not only by the respiration of animals and volcanic action, but by the agency of man himself? In times, perhaps not so very far distant, will not the whole of those vast deposits of coal and lignite, formerly taken from the air, return to the atmosphere again as carbonic acid? And if forests continue to be constantly annihilated, as Mulder remarked, to make room for clay and stone buildings, will not carbonic acid increase, until it once more predominates, as it is supposed to have done in primitive times? It seems evident to me that vitality, nervous power, and atmospheric oxygen have increased together, from the earliest ages of the globe, and that the history of this increase can be read in the records of the Earth's strata. Although, as will be seen presently, my researches bear out this theory of the increase of oxygen in the atmosphere, it presents, at first sight, a curious paradoxical aspect: oxygen is admitted to be the product of life, whilst it is the condition of life, and its final predominance in the atmosphere will, perhaps, be the cause of universal death. Certainly this appears highly paradoxical; and it may be questioned whether the solution of such problems is not beyond the powers of Science, like all those which touch upon creation. But, as I have already remarked, we must distinguish between oxygen, and free oxygen in the atmosphere. B CHAPTER III. Plants are essentially Anaerobic-Experiments by the AuthorPrimitive Atmosphere of the Earth-Vegetation in this Primitive Atmosphere and in other Gases. ADMITTING that no free oxygen could have existed in the atmosphere when life first appeared upon our globe, and that this atmosphere must then have consisted of nitrogen, containing more or less carbonic acid, and vapour of water, it follows that atmospheric oxygen must originally have been derived from the vital functions of inferior plants such as the unicellular algæ, which were the first created beings, having the power, under the mysterious influence of the solar rays, of separating it from its compounds, carbonic acid and water. Granting that the ancient cryptogamic plants of the Coal flora period, for instance, could thrive at higher temperatures, and in an atmosphere far richer in carbonic acid than that of our own day, it became very interesting to ascer tain to what extent our modern plants can vegetate under similar circumstances. It was in making experiments to this effect I dis covered that all plants are essentially anaërobic. I have caused them to vegetate in carbonic acid, in |