The regulation of the supply of oxygen to the tissues 149 



intestine and of the pancreas. But whereas that of the former 

 soon reached its maximum, and assumed its normal volume in less 

 than a minute, the vascularity of the pancreas continued to increase 

 gradually for some minutes ; indeed it was maintained as long as 

 the secretion of the gland (which began about two minutes after 

 injection) continued usually a period of 10 16 minutes." Direct 

 experiments upon the outflow of the blood from the pancreatic vein 

 have given very variable results. 



Before I leave the subject of secretin I must make some allusion 

 to the suggestion of Bayliss and Starling (11) that specific dilatation 

 materials existed for specific organs, for instance extract of jejunum 

 causes dilatation of the intestine but has no effect on the kidney. 

 Their statement of results however was rather of the character of a 

 preliminary communication. 



FIG. 80. Connexions of heart perfused from another animal. A, tube leading from 

 carotid artery of perfusing animal, into this drugs may be injected. B, tube leading 

 to jugular vein of perfusing animal. Samples from the heart are taken at E. The 

 clip is then removed from D and placed at C. 



The heart. The heart presents a very close analogy in some 

 respects to the stibmaxillary gland ; this analogy has in fact been one 

 of the current themes of physiological discussion, its tissue like the 

 secreting tissue of the submaxillary gland has a double nerve supply ; 

 by playing upon this it is possible to increase or to decrease the 

 activity of the heart : we are face to face with the question, Do these 

 changes in activity alter the blood flow through the coronary system 

 and, if so, by what mechanism are the alterations brought about ? 



In our research on the gaseous exchange of the heart, Dixon and 

 I (12) arrived at some data with regard to the functional regulation of 

 its blood flow, The arrangement of the experiment was as follows : 



