254 Chapter XVII 



differences which the diminished CO 2 pressure would produce ? Could 

 we, in short, by the same methods detect any difference in the dis- 

 sociation curves of our blood when exposed at sea- level to the two 

 carbonic acid pressures which obtain in the body at, say, Berlin and 

 Alta Vista ? This is a simple experiment to try. I have here three 

 cubic centimetres of blood withdrawn by means of a needle from one 

 of the large subcutaneous veins in Prof. Zuntz's arm. I divide the 

 blood into two portions, the dissociation curve of each is determined, 

 one in the presence of 35 mm. CO 2 , the other in the presence of 

 23 mm. C0 2 , the alveolar C0 2 pressures at Berlin or Orotava and 

 Alta Vista respectively. The difference in the dissociation curves 

 is evident enough. 



Moreover, the same is clear in the case of Douglas where the 

 disparity of tensions was not so obvious. It is shown in Fig. 122 in 

 which the dotted curve corresponds to Douglas's normal blood 

 exposed to 34 mm. CO 2 . In Zuntz's case the tension at Alta Vista 

 was only two-thirds of what it was at Orotava in Douglas's case 

 it was about three-quarters ; but it is perfectly clear that the same 

 blood exposed to these different tensions gives dissociation curves 

 which are distinguishable from one another with ease and certainty. 

 What then are we to say ? In Berlin the same blood exposed to CO 2 

 tensions of 23 and 35 mm. respectively gives quite different curves, 

 yet the blood of the same individual exposed to 35 and 23 mm. 

 C0 2 tension in Orotava and Alta Vista respectively gives quite iden- 

 tical dissociation curves. 



There is only one conclusion : as we ascend, the C0 2 has been dis- 

 placed in the blood by something else which produces an equal effect 

 on the affinity of the haemoglobin for oxygen. Probably this something 

 else is another, but not a volatile, acid ; it is something which does not 

 go away in the breath. It follows from what we have said above that 

 we should be able to discern its presence. When we were in Teneriffe 

 we did not fail to try. With Orbeli (3) I repeated the experiment when 

 we arrived home by subjecting cats to a diminished oxygen pressure. 

 In the interval between the Teneriffe expedition and the Monte Rosa 

 expeditions Mathison worked out the method for estimating the 

 amount of acid so thrown in the blood. We used this method and 

 made estimations by it and by other methods at Monte Rosa. Up to 

 a certain point the matter is perfectly clear. Let us say what there 

 is to be said about it. We will take up the points in the order 

 in which we have enumerated them : 



