The regulation of the supply of oxygen to the tissues 155 



From this experiment which we have repeated on several occa- 

 sions it would appear that CO 2 is not the only, nor is it the most 

 powerful dilating metabolite. 



Before leaving the subject of the automatic supply of blood to 

 the tissues there is one aspect of it which must not be overlooked. 

 The metabolic products continue to exercise their influence for some 

 little time, amounting perhaps to minutes, after the functional 

 activity of the organ has passed off. Whether we call this a happy 

 accident or a beautiful mechanism it matters not, so long as we 

 understand the true inwardness of the facts which we are studying. 

 For the demand of the organ for oxygen is essentially something 



10 



FIG. 84. Bates of pulse and CO., excretion and blood How from the coronary system. 



which follows upon the activity of the organ, not something which 

 causes the activity nor yet something which absolutely synchronises 

 with it. The time relations of the activity of an organ and the 

 oxygen used up in it make a story which I have already told. So 

 far as can be gleaned from muscle and from the submaxillary gland, 

 organs which by means of nervous stimuli can be thrown instan- 

 taneously into violent activity, activity which can be suspended 

 almost as rapidly by a cessation of the stimuli, it would appear 

 that contraction of the muscle or the secretion in the gland is not 

 itself a manifestation of oxidation in the sense that the work of an 

 internal combustion engine is a direct manifestation of the oxidative 



