652 PHYSIOLOGY OF RESPIRATION. 



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 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 

 of the extent or character of the physiological oxidations in the body, 

 since any alteration in the depth or rapidity of the respiratory 

 movements may, by changing the ventilation of the alveoli, make 

 a difference in the output of CO 2 , a difference, however, which 

 would have no significance in regard to the nutritive changes of the 

 body. In longer experiments and in those during which the respira- 

 tory movements are not altered the determination of this ratio 

 throws light upon the character of the oxidations that are taking 

 place, as will be apparent from the following considerations : Under 

 ordinary conditions of rest and upon a mixed diet the R. Q. varies 

 between 0.65 and 0.95 (Loewy) or between 0.75 and 0.89 (Magnus 

 Levy). If, however, the material oxidized in the body is entirely 

 carbohydrate the R. Q. should be equal to unity: ^ 2 = 1. All the 

 oxygen used in the combustion might be considered as uniting with 

 the C to form CO 2 , since enough O is present in the sugar to account 

 for that used in oxidizing the H to H 2 0. Or, as expressed in a 

 reaction, 



Dextrose. 



C 6 H 12 O 6 + 6O 2 = 6C0 2 + 6H 2 O. R. Q. = = 1. 



The number of molecules of C0 2 formed in the oxidation is equal 

 to the number of molecules of O 2 used. If fats alone are oxidized 

 in the body the R. Q. should be low (0.7), since these substances 

 are poor in oxygen compared with the amount of C and H present 

 in the molecule. The combustion of palmitin may be represented 

 as follows: 



Palmitin, C 3 H 5 (C 16 H 31 O 2 ) 3 = C^H^O.. 

 2(C 51 H 88 O a ) + 145O 2 = 102CO 2 + 98H 2 O. 



R. Q. = ill = o.7. 



