474 PHYSIOLOGY CHAP. 



the regulating factors less complex. It is clear that if the 

 ordinary respiratory mechanism were not, within certain limits, 

 independent of the chemical needs of the body, or the gas content 

 of the blood, then " at every change of the barometer (some of 

 which are enormous) every man and every animal would have 

 suddenly to alter both frequency and depth of respiration, in order 

 to equalise the changes in the atmosphere " (Mosso, 1898). 



Here, however, we touch upon new problems, which demand 

 solution. For if we accept this theory of eupnoea, it may be 

 asked : " What are the external factors causing this excess of 

 pulmonary ventilation? If in the dyspnoea from hard muscular 

 work, pulmonary ventilation increases to oppose the increased 

 venosity of the blood, and if this effect exceeds the immediate 

 requirement, must not the same effect occur in eupnoea, and the 

 venosity of the blood diminish to such an extent that it would in 

 a short time become inadequate to maintain the activity of the 

 centres ? If, in order to explain the dyspnoea of work, we are 

 obliged to invoke the presence of a (probably acid) waste product of 

 muscle in the blood, capable of sur-exciting the respiratory centres, 

 are we not equally obliged to admit that an analogous product 

 may be acting in eupnoea, stimulating the activity of the centres, 

 and raising the respiratory capacity (by about one-half) beyond 

 the immediate need ? 



Again, how does the chemistry of respiration alter at high 

 altitudes where luxus-respiration ceases ? 



According to the analyses of blood gases made on the dog by 

 Frankel and Geppert (1883) to test the effect of varying baro- 

 metric pressures, in air rarefied to a pressure of 410 mm. the 2 and 

 C0 2 content of arterial blood is not perceptibly altered ; and at a 

 pressure of 198 mm. the loss of gases from the blood is still extremely 

 small (1 part 2 and T65 part C0 2 ). Mosso attributes great 

 importance to this relatively minute diminution of the C0 2 of the 

 blood. He believes it to represent a state of the blood contrary to 

 that which prevails in asphyxia, and proposes to call it acapnia, 

 holding it to be one of the causes of mountain sickness. This 

 conclusion seems to us to be premature and hazardous. "We admit 

 that acapnia, or the abnormal diminution of C0. 2 in the blood, can 

 only be regarded as the effect of two opposite processes, either, i.e., 

 of a diminished production of C0 2 , as in sleep, or of its augmented 

 excretion, as in artificial or forced voluntary respiration. Now 

 neither the one nor the other condition of' acapnia is fulfilled 

 in respiration at a high altitude above sea-level. From the 

 experiments undertaken by Mosso upon three soldiers, after they 

 had rested, so as to exclude the effects of muscular fatigue, it 

 appeared that "no important modification in the elimination of 

 CO 2 and^the volume of respired air can be detected at high 

 altitudes/- This proves that even in rarefied air " the organism 



