RESPIRATION 1 1 



scarlet as arterial ; and with the blood pump we can easily prove 

 that the scarlet blood contains more dissociable oxygen than the 



blue. 



Rosenthal came to the conclusion that it is solely or almost 

 solely in virtue of its varying oxygen content that the blood, 

 stimulates the respiratory center or not.^^ Careful blood-gas de- 

 termmations showed that when apnoea had been produced by 

 forced ventilation of the lungs the arterial blood contained a little 

 more oxygen. On the other hand, when oxygenation was rendered 

 incomplete by letting an animal breathe air very poor in oxygen 

 there was an immediate great increase in the breathing, although 

 the discharge of carbonic acid was in no way interfered with. 

 Moreover, when air containing; a^verj laj^ejexcess pi_C.O^^^^ 

 breathed byTin aniniar the rate oFbreatliing remained normal. 

 Rosenthal also brought forward other evidence which appeared^ 

 to point in the same direction ; but the weak point in his argument 

 was the fact that there is no apnoea when pure oxygen is breathed, 

 although the arterial blood contains a good deal more oxygen 

 than usual. The truth is that he had been misled by the fact that a 

 very high percentage of CO2 in the air breathed has a narcotic 

 effect, so that the breathing, which is in reality increased at first 

 by raising the percentage of CO2 in the air of the lungs, quiets 

 down again when the percentage becomes very high. Pfliiger and_ 

 Hohmen^''' showed that both excess of CO2 (provided that the CO2 

 is not in too great excess) and want of oxygen excite the respira- 

 tory center. 



A further fact, discovered originally by Traube,^^ but often 

 overlooked by subsequent investigators, was that apnoea could 

 big^'pr^HuceH^yeifBy a gas as hitfogen or hydrogen, in whrch 



no oxygen was present. Thus if apnoea is due to *'over-arterializa- 

 fion^^f the arterial blOod"it can be produced by the simple re- 

 moval of CO2, whether or not the oxygen is also diminished, 

 although the artificial ventilation of the lungs must be much more 

 vigorous if apnoea is produced in the absence of oxygen. 



Meanwhile another theory of apnoea was put forward, and 

 has'leH^ as will be shown later, to the utmost corifusion and com- 

 plete misinterpretation of the facts. When the lungs are distended 

 there is, as already mentioned, an interruption in the rhythm of 

 discharge from the respiratory center. The inspiratory muscles, 



^"Rosenthal in Hermann's HancLbuch der Physiol., Vol. IV, 2, 1882. 



"Pfliiger, Pfluger's Archiv, I, p. 61, 1868. 



" Traube, Allgem. Med. Centralzeitung, 1862, No. 38, and 1863, No. 97. 



