PULSE-RATE. 383 



which must first be thoroughly cleared by careful accumulation of 

 experimental evidence. Diastolic blood pressures so close to the shock 

 level as those observed with several of these men would imply that the 

 dietetic conditions in this research might be somewhat near the border 

 line of safety. Obviously, low blood pressure brought about by dietetic 

 alterations must be thoroughly studied in all its phases before final 

 deductions can be made. 



PULSE-RATE. 



The intimate relationship between the mechanism of the circulatory 

 system and the total metabolism has been frequently pointed out in 

 pubhcations from the Nutrition Laboratory. The heart rate is, with 

 the same individual, a remarkably significant index of the total 

 metabolism. When it is considered that the total carbon-dioxide 

 production is directly proportional to muscular activity and heat 

 production, and furthermore that the blood must carry away the 

 carbon dioxide and supply fresh oxygen to the tissues, in proportion 

 to the need therefor, it is not surprising that the work of the heart 

 bears a general relationship to the total metabolism. If the systoHc 

 discharge from the heart were uniform under all conditions, one could 

 predicate that the pulse-rate would be proportional to the total 

 metabolism. Such a proportionality of relationship, however, is by 

 no means established or to be inferred from experimental evidence thus 

 far obtained. 



While a reasonably close correlation between the pulse-rate and the 

 total metabolism of a given individual appears to be substantiated 

 by a large number of experiments, this does not apply in any sense to 

 a comparison of the pulse-rate and total metabolism of different 

 individuals. For example, when a subject has a pulse-rate of 60 at one 

 time and a pulse-rate of 80 at another time, one can be sure that the 

 metabolism will be measurably higher with the higher pulse-rate, but 

 it is by no means certain that subject A with a pulse-rate of 60, even 

 with an equivalent weight and height, will have a metabolism lower 

 than subject B of the same height and weight with a pulse-rate of 80. 

 Indeed, the absence of correlation between pulse-rate and total metab- 

 olism with different individuals has been frequently noted and com- 

 mented on in this Laboratory. On the other hand, a recent biometric 

 treatment^ of the basal metabolism data of the Nutrition Laboratory 

 has indicated the existence of a slight but apparently significant corre- 

 lation between these two variables, sUghtly higher gaseous exchange 

 being associated with higher pulse-rate, even with men and women in 

 complete muscular repose and in the post-absorptive state. 



In this research on low diet it was imperatively necessary to ob- 

 tain every possible index of metabolism or physiological activity 



i Harris and Benedict, Carnegie Inst. Wash. Pub. No. 279, 1919, p. 79. 



