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402 a poverty of the blood-corpuscles in oxygen, which. lie believed to be a result of the feeble pressure of the atmosphere in those regions. In the study of the question of the influence of atmospheric pressure on health, which he was led by these observations to undertake, he availed himself of the aid of M. Bert's experimental skill. M. Bert performed a long series of experiments upon small animals exposed to atmospheres of various pressures. The book in which he gave an account of them includes full reviews of excursions into great altitudes, of observations on mountain-sickness, and of balloon ascensions to great heights. An experimental ascension in the balloon Zenith was made in 1875 in aid of this investigation, its special object being to determine the quantity of carbonic acid contained in the atmosphere at an altitude of twenty-four thousand feet. Three persons went up in the balloon, two of whom, M. Sivel and M. Crocé Spinelli, perished at a height of about twenty-four thousand feet, from the effects of the rarefied air, while the survivor, M. Gaston Tissandier, was made insensible for a considerable length of time. The main cause of the disaster was believed to be "the vertigo of high regions," by which the aeronauts were excited to throw out ballast and go higher, when prudence should have dictated to them to descend. The main object of the expedition was not attained, because the instruments also were thrown out and broken. The balloon reached a height of eight thousand six hundred metres, as was shown by the maximum barometers. The results of Prof. Bert's experiments were published in 1878, in his work "La Pression barométrique; Recherches de Physiologie expérimentale" ("Barometric Pressure; Researches in Experimental Physiology"). Among his principal conclusions were those that the diminution of barometric pressure acts on living beings only by diminishing the tension of the air which they breathe, in the blood which animates their tissues, and by thus exposing them to the dangers of asphyxia; that the increase of atmospheric pressure acts only by increasing the tension of the oxygen in the air and the blood; that the inconvenient effects of diminution of pressure may be efficaciously combated by the respiration of an air sufficiently rich in oxygen to maintain the tension of that gas at its normal value, and those of the increase of pressure may be combated by employing air sufficiently poor in oxygen to arrive at the same result; that the beings actually existing in a wild state on the surface of the globe are accommodated to the degrees of oxygenated tension under which they live; that barometric pressure and the proportion per cent of oxygen have not always been the same on our globe—the tension of the gas has apparently been, and will without doubt continue to go on, diminishing; and that it is inaccurate to teach that plants must have appeared on the earth