PHYSIOLOGICAL CHANGES IN TRANSITION. 299 



similar character, which were made subsequent to this work and re- 

 ported by Benedict, Miles, Roth, and Smith, 1 showed like irregularities 

 which were explained by the investigators as due in all probability to a 

 psychical stimulus occasioned by the warning signal for starting. 

 Though no signal for starting was given in the experiments here rep- 

 resented, the explanation may apply to these curves also, for the sub- 

 ject was naturally conscious that walking would begin at any moment, 

 as there were certain routine movements which he would recognize as 

 preceding the start. These irregular factors of duration have one 

 noticeable feature in common, namely, one or more points of a retarded 

 pulse, i. e., of lengthened duration. It does not appear that the 

 lengthening was in any way related to the beginning of walking, 

 though one might expect that it marked the period when the subject 

 realized that the operator was ready to open the air-valve and start 

 the treadmill. 



It is also apparent from these curves that the average cycle duration 

 shortened uniformly during walking to a minimum duration which was 

 reached in from 150 to 200 cycles, the greater portion of this change 

 occurring in the first 100 cycles, with the change gradually diminishing. 

 On two days (see curves A and B), a slight tendency to a reaction set 

 in at approximately 100 cycles. The time when the minimum dura- 

 tion was reached is seen to be approximately 1 minute and, except in 

 curve C, this minimum was held with a considerable degree of con- 

 stancy in the remainder of the record, i. e., to the end of the second 

 minute. It is thus evident that the pulse-rate increased to meet the 

 demand of the added work placed upon the body within approximately 

 150 cycles and with a time lapse of between 1 and 2 minutes. Beyond 

 this point there would undoubtedly be some rise and some variation, 

 but the greater part of the pulse change occurred in the first minute 

 for the conditions of work illustrated here. 



To compare the pulse-cycles over greater intervals of time, a more 

 extended record of five curves is given in figure 40. In these records 

 we have attempted to measure the individual cycles and each point 

 represents the average of 2 cycles thus measured. Since under these 

 conditions there is more or less error in the estimation of fractions of 

 time intervals, not a little of the irregularity shown in the pulse-cycles 

 for standing may be due to this cause. Curve A in figure 40 is a record 

 taken during the middle of a standing period at 9 h 44 m a. m. on Feb- 

 ruary 28, 1916. Even allowing for the errors of measurement, it is 

 evident that during standing there were constant fluctuations in the 

 duration of the pulse-cycle like those found in the standing portions of 

 the curves in figure 39. Between the minimum and maximum dura- 

 tions there was a total difference of 0.34 second, this change occurring 

 within 8 cycles. The second curve (B), which is not continuous with 

 curve A, includes the transition from standing to walking. Like the 

 curves in figure 39, the standing portion, which is indicated by the re- 

 Benedict, Miles, Roth, and Smith, Carnegie Inst. Wash. Pub. No. 280, 1919, p. 429. 



