416 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



the subjects in the low-diet research began somewhat early to exhibit 

 radial pulse-rates which were notably below those of normal, it ap- 

 peared to us particularly important to examine the change in heart 

 rate with exertion. An accurate and at the same time the most con- 

 venient method of securing records which will provide information 

 of this sort is to take electrocardiograms by the technique described 

 on page 152, i. e., with body electrodes connecting the subject to the 

 string galvanometer for the taking of continuous records while he is 

 quiet, active, and again at rest. The sample records, which are illus- 

 trated in figure 24 (see page 152), demonstrate clearly that any consid- 

 erable irregularity in the rhythm or conduction of the electrocardiogram 

 under these conditions could be readily discovered, except perhaps 

 during the actual moments of exertion, when only the prominent R 

 deflection is legible in the tracing. The auricular wave P is usually very 

 small, partly because of the capacity and resistance in series in the 

 circuit reducing the amplitude of the deflections. The P wave is, 

 however, usually indicated in the quiet pulse prior to exertion. It 

 also becomes visible in the latter part of the recuperation period, and 

 since the ventricular complex (R and T waves) appears with increased 

 frequency between the two points in the record where the P wave is not 

 evident, it is probable that all of the impulses are of sinus origin and 

 proceed in the normal way. No stress can be laid upon the shape of 

 the waves. Only their order and frequency concern us here. 



To secure an accurate measure of the length of the pulse cycle, we 

 measured from the sharp point R to R.^ A table for all the pulse- 

 cycle data shown n these records would be very large and unwieldy. 

 Data of this character for a series of similar electrocardiograms taken 

 on one subject have been published elsewhere.^ Each individual pulse 

 cycle (R to R distance) is measured, the unit being 0.01 second. In 

 discussing such pulse changes, it is more logical to use pulse-cycle 

 length than pulse-rate per minute. The two statements must not be 

 confused. The data can be conveniently presented in the form of 

 curves. An illustrative set of curves for an individual subject is given 

 in figure 92. Records were taken for Mon on the five days, October 28, 

 November 11, December 9, January 13, and January 27. In order to 

 avoid a confused diagram, curves for only three dates are given, those 

 for November 11, December 9, and January 27. In each case the curve 

 is the average for two similar and consecutive records, separated by one 

 minute or more of rest. The portion of the curve to the left of the 

 heavy vertical line represents the period of quiet rest in the steamer 

 chair. The pulse-cycle length varies somewhat, as is to be expected in 

 any normal individual, due to the respiratory changes and other influ- 

 ences on the vagus. No signal or indication was given to the subject 



1 Miles, Carnegie Inst. Wash. Pub. No. 266, 1918, p. 95. 

 * Miles, ibid., p. 98, table 17. 



