126 GASEOUS METABOLISM OF INFANTS. 



EFFECT OF CHANGES IN ACTIVITY ON THE PULSE-RATE AT DIFFERENT 

 AGES WITH THE SAME INFANT. 



The extreme sensitivity of the pulse-rate to major changes in muscu- 

 lar activity has already been shown, but it is also important to note 

 whether or not this sensitivity altered materially with increasing age. 

 With one of the infants, J. V., we were able to make observations when 

 she was 3| months old, with a body-weight of 1.9 kilograms, and again 

 when she was 7| months old, with a body-weight of 3.3 kilograms. 

 The curves obtained on January 25 and on May 27 are therefore 

 compared in figure 38. 



.130 ll8 »6 



Fig. 38. Pulse-rate curves with J. V. 



a. January 25, 1.9 kilograms, 3j months, awake and crying vigorously, restless, quiet (asleep). 

 6. May 27, 3.3 kilograms, 7? months, moving and grumbling, then quiet. 



c. January 25, 1.9 kilograms, 3^ months, quiet (asleep), moved, cried, restless, cried. 



d. May 27, 3.3 kilograms, 1\ months, quiet, moving, moving and grumbling. 



In the period covered by the first curve (a) for January 25, i. e., from 

 3 h 35 m p. m. to 4 h p. m., the infant was at first awake and restless, then 

 quieted down until she fell asleep. The pulse-rate fell from 168 to 130 

 per minute during this period. The second curve for this day (c) shows 

 a change in the pulse-rate from 118 at 4 h 18 ra p. m., when the infant was 

 quietly sleeping, to 151 at 4 h 36 m p. m., when she was awake, restless, 

 and crying. In the first instance the fall in the pulse-rate of 38 beats 

 required 25 minutes; in the second instance the rise in the pulse-rate of 

 33 beats took place in 18 minutes. 



On May 27, the records (curve b) show that the pulse-rate fell from 

 149 at 3 h 14 m p. m., when the child was moving, to a minimum of 118 

 at 3 h 36 m p. m., when it was quiet, or 31 beats in 22 minutes. The 

 second record for this day (curve d) shows a rise in the pulse-rate when 

 the infant woke up and cried from 1 14 at 5 h 06 ra p. m. to 147 at 5 h 22 m p.m., 

 or an increase of 33 beats in 16 minutes. 



Comparisons of this kind are always complicated by the possible 

 variation in the intensity of the activity, although in the instances 

 selected the external activity seemed to be essentially the same under 

 the various conditions. There was no evidence of greater sensitiveness 

 in the later observations, but there was a distinct tendency for the 

 minimum pulse-rate at the age of 7| months to be somewhat lower than 

 at the age of 3| months. 



