The regulation of the supply of oxygen to the tissues 137 



branches of the portal vein. We have therefore a complete scheme 

 before us. The regulation of the portal blood depends upon the 

 intestine and on the processes going on in the intestine. So far 

 as the liver is concerned the portal blood is the raw material on 

 which it works, but it has also a blood supply proper to itself for the 

 needs of its own metabolism. 



Now to turn to the general question of the fluctuations which 

 occur in the blood supply of the organs of the body. We are not 

 concerned with such fluctuations as are brought about by the central 

 nervous system without reference to the needs of the organ for the 

 purpose of maintaining the general arterial pressure. These do not 

 touch the respiration of the organ. In Chapter V we have emphasised 

 the great variations which occur at different times in the need of the 

 organ for oxygen. Unless the tissue when at rest is to be flooded 

 with large quantities of unnecessary blood, the variations in its blood 

 supply must be of the same order as those of the oxygen required. 

 And for our present purpose we must regard the question of blood- 

 flow from the point of view of the oxygen itself. 



Let us take the pancreas as an instance. It is excited to activity 

 by a stimulus which acts directly upon its cells ; the gland at once 

 requires four or five times as much oxygen as before : how is this to 

 be obtained ? Is there a reflex mechanism by means of which the 

 pancreas can beg a supply of blood from the vaso-motor centre? 

 We know of none. Does the secretion act on the vaso-inotor centre 

 itself ? We have no reason to suppose that its action is anything but 

 local. The broad question which is to be answered is this, Is there 

 evidence that each organ of the body is so far master of its own 

 metabolism that it can force the vascular system to give it the oxygen 

 which it requires ? 



This is the sort of question which used to be put by Gaskell to his 

 class when I was a student ; since then the evidence on the subject 

 has increased many fold. 



Let me start then by accepting (1) the conclusions of Severini (3) , 

 Gaskell (4) , and other more recent workers, in so far as they show that 

 certain products of metabolisms, to wit acids including C0 2 and lactic 

 acid, have the power of distending blood vessels, and (2) those of 

 Dale (5) and his colleagues to the effect that /3-iminazolylethylamine, a 

 body so closely bound up with the physiology of protoplasm that it is 

 liberated by the splitting off of C0 2 from histidine, will produce a 

 powerful dilatation of the vessels. So powerful indeed is the effect 



