The regulation of the supply of oxygen to the tissues 145 



That the "chorda blood" is richer in acids as compared with 

 alkalis, than either the arterial blood or the venous blood, is doubly 

 manifest. The first method of demonstration is essentially that used 

 by Morawitz namely, analysis shows that in equilibrium with 

 carbonic acid at a given pressure the chorda blood contains less 

 C0 2 than the ordinary venous blood, which in turn contains less 

 than the arterial blood, showing of course that the bases are more 

 completely saturated by other acids. 



Fig. 79 shows the quantity of C0 2 contained in each of the three 

 samples of blood when in equilibrium with the pressures of CO 2 at 

 which the tests were carried out. For a given CO 2 pressure, say 

 41 mm., 100 c.c. of the chorda blood contains 36 c.c. of CO 2 , the resting 

 venous blood 39 c.c., whilst the arterial blood takes up 44 c.c. 



The second method of showing that the chorda blood is the more 

 acid is by the effect on the affinity of its haemoglobin for oxygen. 

 The curves are shown in Fig. 88. 



To summarise our case so far, stimulation of the submaxillary 

 gland by means of adrenalin furnishes us with a case of local dilata- 

 tion as the result of metabolic products, which dilatation can be shown 

 to be complete in every particular : the direct effect of the drug on 

 the vessels is constriction. This constriction is overridden when, and 

 only when, the gland secretes, in that case bodies which are known 

 to cause dilatation are demonstrably produced. 



I do not think anyone can actually see a demonstration of the 

 phenomenon which I have just described without asking himself 

 whether this functional dilatation does or does not explain the whole 

 phenomenon of dilatation as observed in the salivary glands. In 

 other words, is it possible to demonstrate that the vaso-dilatation, 

 which follows upon stimulation of the chorda tympani, involves a 

 definite neuro-muscular vaso-dilatator mechanism ? 



Claude Bernard supposed that when the chorda tympani was 

 stimulated three sets of fibres were thrown into action the calorific, 

 the vaso-dilatator, and the secretory. The evidence of the calorific 

 was of the most direct kind, namely that heat was demonstrably 

 produced when the nerve was stimulated; the evidence of the vaso- 

 dilatator fibres was of the most direct kind, namely that the blood 

 stream was demonstrably accelerated; and the evidence of the secretory 

 fibres was of the most direct kind, namely that the saliva was seen 

 to flow. 



The conception of the calorific fibres has long since gone; the 



B. R. F. 10 



