xiii EESPIEATOEY EHYTHM 475 



requires its normal supply of oxygen," i.e. it consumes the same 

 amount, and therefore eliminates the same quantity of carbonic 

 acid. It may be noted in passing that these facts contradict 

 the preceding data on which Mosso rests his theory of luxus- 

 respiration. 



Eecently (1906) Zuntz, Loewy, F. Miiller, and Caspari, in the 

 course of their numerous researches on the physiological action 

 of climate at high altitudes and of alpine excursions on man, 

 have enumerated a series of observations and data which directly 

 contradict the theory of acapnia. They found, as a matter of fact, 

 that there is in the majority of cases a progressive diminution 

 of C0 2 tension in the lungs in proportion with the altitude. Thus, 

 e.g., while the tension of the pulmonary C0 9 was in Zuntz, at a 

 barometric pressure of 715 mm., 38*5 mm., at a barometric 

 pressure of 689'9 mm. it fell to 32'6, becoming 27'2 at 439'3 mm. 

 barometric pressure. It is, however, true that there is a 

 simultaneous increase of respiratory intensity, i.e. an augmentation 

 of pulmonary ventilation. 



The diminished pulmonary tension of the C0. 2 would thus be a 

 secondary effect of increased ventilation, which in its turn depends 

 upon the diminution of the oxygen in the respired air. 



They further note that not every individual presents the same 

 diminution of CO Q tension in respect of altitude. In one person, 

 e.g., no diminution in C0 2 tension was noted, and yet he was one 

 of those who suffered most from mountain sickness. Others, on 

 the contrary, who exhibited the said diminution, were exempt 

 from sickness. 



In order, at least to some extent, to clear up this uncer- 

 tainty as tro the theory of eupnoea, and the better to define the 

 nature of the relations existing between the chemistry and the 

 mechanics of respiration, i.e. between the gas content of the blood 

 and the capacity of pulmonary ventilation, it will be well diligently 

 to examine the various conditions under which it is possible to 

 observe the phenomenon of apnoea. 



XI. If the rhythmic and alternate activity of the respiratory 

 centres is strictly bound up with the quantity of oxygen and 

 carbonic acid of the blood that is circulating through them, it 

 should be suspended when the venosity of the blood is artificially 

 reduced, so as to render pulmonary ventilation useless. The name 

 of apnoea has been given to such suspension of the respiratory 

 movements when they have become temporarily superfluous. 



Hook (1667) (see p. 371) was the first to observe it, but he 

 formulated no conclusion as regards the process by which the 

 respiratory centres enter into rhythmic activity. The first to 

 study apnoea by making it the basis of the doctrine of respiratory 

 rhythm was, as we have stated, Eosenthal (1862). His work was 

 taken up and enlarged by Pfliiger (1868). 



