144 



Chapter IX 



would have flowed freely, and the constriction would rapidly have 

 been overridden by dilatation. 



It remains for us to see whether there are as a matter of fact bodies 

 secreted into the blood which are capable of dilating the vessels. 

 The bodies which are capable of causing dilatation may be divided 

 into two groups from our present point of view : (1) acids, (2) organic 

 bases, such as those isolated by Dale and Barger. The latter 

 act in extremely minute quantities, and nothing would appear more 

 probable than that such bodies should be produced in small quantities 

 in the breakdown of tissues. It is a commonplace that extract of 

 almost any organ produces such substances ; their very commonness 



10 



25 30 35 40 ~ 45 50 55 60 



FIG. 79. Ordinate^c.c. of CO., per 100 c.c. of blood. Abscissa=C0 2 pressure in mm. 



has caused them to be largely overlooked in comparison with pressor 

 substances. It is certain that such substances may be obtained from 

 the submaxillary gland. 



On the other hand, as regards the reaction of the blood, there are 

 special reasons why the fluid bathing the cells should be less alkaline 

 when the gland is secreting than when it is not doing so. The secretion 

 of the submaxillary is, of course, strongly alkaline. This means that 

 the bases are taken from the lymph and secreted whilst the acids are 

 thrown back into the blood. We can test the question experiment- 

 ally. We find that the blood in its passage through the gland does 

 actually change its hydrogen ion concentration, and it would there- 

 fore seem that the lymph in equilibrium Avith it cannot but dilate 

 the vessels. 



