714 PHYSIOLOGY OF RESPIRATION. 



ments to show that there is a diminution in the carbon dioxid 

 contents of the blood (a condition of acapnia), and it is to this, 

 rather than to the anoxemia, that he would attribute the physio- 

 logical results of low barometric pressures. Other authors lay 

 stress upon the mechanical disturbances of the lung circulation, 

 while still others assume that certain vaguely understood cosmical 

 influences such as the electrical condition of the air, its ioniza- 

 tion, or radiations of some kind may affect the metabolisms of 

 the body. The balance of evidence, however, indicates that the 

 chief factor in the production of mountain sickness is deficiency 

 in oxygen, particularly when the oxygen need of the body is in- 

 creased, as, for example, in muscular exercise. Experiments seem 

 to show that the total amount of oxygen in the arterial blood may 

 not be diminished, owing to the greater percentage of hemoglobin, 

 but the hemoglobin is less saturated, and the oxygen is under a 

 lower pressure and, therefore, it is not supplied so rapidly to the 

 tissues. At very high altitudes the supply of oxygen for the body 

 exhibits only a small margin of safety, and we may suppose that 

 relatively little muscular exercise, with its attendant increase in 

 oxygen consumption, will suffice to deplete the supply to such an 

 extent as to affect the brain centers* The historical incident 

 of the death of Sivel and Croce"-Spinelli at an altitude of 8600 

 meters (barometric pressure, 262 mms.; oxygen pressure, 52.4 mms.) 

 gives an impressive instance of the physiological effects of extreme 

 altitudes. 



The incidents connected with the ascent in the balloon Zenith of Sivel, 

 Croce-Spinelli, and Tissandier, April 15, 1875, are described in detail by the 

 last named in "La Nature," 1875, p. 337, also in Bert's "La pression baro- 

 metrique," p. 1061. Only Tissandier survived. The balloonists were pro- 

 vided with bags containing oxygen (72 percent.), but they were unable to 

 make satisfactory use of them since shortly after passing 7500 meters they be- 

 came so weak that the effort to raise the arm to seize the oxygen tube was 

 impossible. Tissandier's graphic description relates that at 8000 meters 

 it was impossible for him to speak, and that shortly afterward he became 

 entirely unconscious. None of the three seems to have shown any signs of 

 violent dyspnea. It is noteworthy, however, that the heart-beats were very 

 rapid, and that they experienced at first great depression of muscular strength 

 without loss of consciousness. The onset of complete unconsciousness was 

 sudden, but was preceded by feelings of sleepiness, which, however, were not 

 associated with any distress. 



The Respiratory Quotient and its Variations. In studying 

 the gaseous exchanges of respiration one may determine the varia- 

 tions in the oxygen absorbed under different conditions or in the 



carbon dioxid eliminated, or finally in the ratio of one to the other, 



c*o 



-Q-*, which is known as the respiratory quotient. In short-lasting 



experiments the respiratory quotient is not a very reliable indicator 



