708 PHYSIOLOGY OF RESPIRATION. 



stress upon the mechanical disturbances of the lung circulation, 

 while still others assume that certain vaguely understood cosmicai 

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

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

 the body and thus produce the symptoms in question. It would 

 seem that the whole matter is more complex than was at first 

 supposed, but the balance of evidence indicates that the chief 

 factor in the production of mountain sickness is deficiency in 

 oxygen, particularly when the oxygen need of the body is increased, 

 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 probably 

 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 

 the violent dyspnea that usually precedes asphyxia caused by lack of oxygen. 

 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. These latter facts recall the conditions of " shock, " and 

 would suggest that probably the rapid heart beat was an indication of a great 

 fall in blood-pressure, which may have been directly responsible for the mus- 

 cular weakness and final unconsciousness and death. 



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, 

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

 experiments the respiratory quotient is not a very reliable indicator 



