114 PHYSIOLOGY OF THE NEW-BORN INFANT. 



the metabolism was specifically studied, 1 but in the research on the 

 metabolism of new-born infants, the recording of the pulse-rate was 

 only incidental to the measurements of the metabolism and a special 

 assistant was not assigned to this routine; the method of taking the 

 records was therefore somewhat defective. Nevertheless, from 6 to 8 

 observations were made during each 30-minute period and a sufficient 

 number of periods were used in averaging to give reasonable assurance 

 of the validity of the average values obtained. A study of the pulse- 

 records is therefore desirable. 



The observations of the pulse-rate in the previous research showed 

 the very wide variations which may reasonably be expected to occur 

 in a short period. The infants studied at that time included only a 

 few new-born infants, yet the records obtained in the later research 

 show the same striking changes in the pulse-rate that were found with 

 the older infants. This may be seen in table 17, 2 in which the average 

 pulse-rates for the periods of minimum metabolism are given and com- 

 pared with those for the periods of maximum metabolism. It should 

 be borne in mind that these values do not represent the minimum or 

 maximum pulse-records, but only the average pulse-rates for those 

 periods in which the minimum or maximum metabolism was found for 

 the individual infants. The comparison of the values obtained in 

 these periods has a special interest in our study of the minimum and 

 maximum metabolism of new-born infants. 



The values for the pulse-rate during the periods of minimum metab- 

 olism ranged from 86 for infant No. 90 to 132 for infant No. 48, the 

 average for the 93 subjects being 112. When we examine the average 

 values for the periods of maximum metabolism, certain anomalous 

 values are apparent, but usually the pulse-rate for the minimum period 

 was distinctly lower than that found during the maximum period, the 

 average value for the maximum period being 129, or 17 beats higher 

 than the average value for the minimum periods. Very great differ- 

 ences are, however, frequently found between the highest and lowest 

 values. For instance, with infant No. 6 the pulse-rate for the maximum 

 period was 160 and for the minimum period 116, and with infant No. 8 

 the averages were 162 and 117 respectively. With infant No. 73 a still 

 greater difference was found, the values being 162 for the maximum 

 and 106 for the minimum; essentially the same values were found for 

 infant No. 89, with whom the metabolism increased 211 per cent. We 

 may say with perfect propriety, therefore, that in general with new-born 

 infants the pulse-rate increases with the metabolism, but we do not 

 find so close an approximation to the mathematical relationship 

 between the increment in the pulse-rate and the metabolism as was 

 observed with the fasting man recently studied in this laboratory. 3 



'Benedict and Talbot, Carnegie Inst. Wash. Pub. No. 201, 1915, p. 130. 



2 See page 112. 'Benedict, Carnegie last. Wash. Pub. No. 203, 1915, p. 350. 



