SUMMARIES AND CORRELATIONS. 255 



the circulatory system responds with great delicacy and complexity 

 of adjustment to waves of nervous excitation is an empirical fact. But 

 the mechanism of those adjustments is as little known to us as the 

 nervous conditions of thought itself. As mere expressions of mental 

 states they probably have no peculiar analytic function in psychology 

 which may not equally well be assumed for a considerable number of 

 involuntary muscles and glands. 



The biological function of the circulatory system, however, gives it a 

 unique connection with the nervous as well as with the muscular activi- 

 ties of the body. Since the blood-currents supply the conditions of all 

 metabolism, in any adequately organized body within the limits of 

 physiological efficiency there must be a general correspondence between 

 need and supply. This theoretical assumption is borne out by the 

 experimental evidence. Muscular activity in any part of the body 

 almost immediately increases the heart-rate over the rate during relax- 

 ation. In any individual under normal circumstances, the heart-rate 

 is more or less closely proportional to the amount of activity. 



Apparently for considerable periods of sustained work the corre- 

 spondence between metabolism and the heart-rate is much closer than 

 for short periods. Grounds for the unreliability of short periods are 

 easily discoverable. The biological correspondence between need and 

 response can not be a cooordinate or a preliminary adjustment. No 

 automatic vasomotor or cardiac excitation could be based on prophecy 

 of action without the need of constant readjustment. No adjustment 

 could be based on the actual need without a certain lag of latent time. 

 So whatever the mechanism, whether one of preparation or one of 

 reaction, we would expect oscillatory variations about the line of actual 

 need. This gives rise to a serious limitation of the use of heart-rate as 

 an indicator of metabolism in mental activity. To assume that the 

 intense disturbances of short duration that occur in emotion exactly 

 correspond to metabolic demands would be unwarranted by any of 

 the present evidences of correlation. It is not impossible. Since the 

 emotions represent moments of active readjustment, there is some 

 ground for suspecting that they will make their own peculiar demands 

 on metabolism. But correlations are matters of fact, not of probability. 

 A direct study of metabolism would seem to be a desideratum in the 

 dynamic psychology of the emotions. Similarly, to assume that every 

 change in the heart-rate is significant of some definite though uncleared 

 mental state would be unwarranted. Lehmann some time ago aban- 

 doned his early supposition to this effect. The rhythmic changes in 

 heart-rate due to respiration give an illustration of the danger of 

 attempting to isolate short intervals experimentally. 



Furthermore, the pulse-rate never gives direct and absolute values- 

 only relative and comparative. The pulse of muscular work is com- 

 monly known to be both larger and faster than that of muscular 

 relaxation. The amount of acceleration produced by any given quan- 



