130 GASEOUS METABOLISM OF INFANTS. 



RELATIONSHIPS OF THE MUSCULAR ACTIVITY. PULSE-RATE. AND METABOLISM. 



It has been a fundamental principle in all of our previous experi- 

 menting, with both adults and animals, that only periods of complete 

 muscular repose should be used for comparison in studying the metab- 

 olism. The observations made with infants were also based upon 

 this principle, the index used being the graphic records obtained with 

 the mechanical registering device previously described. While for the 

 major purposes of this publication, quiet periods were sought and the 

 metabolism during periods of restlessness was only incidentally studied, 

 we obviously unintentionally secured a large number of periods of more 

 or less muscular activity. The relationships for the various muscular 

 activities of the infant, the pulse-rate, and the total metabolism may 

 therefore be readily discussed. To this end, a number of kymograph 

 curves are reproduced in figures 43 to 48, showing the muscular activity 

 of several infants. 



From a consideration of the mechanical principles of the swinging 

 crib, it can be seen that the heaviest and strongest infants would 

 produce the greatest amplitude of vibration of the crib, this vibration 

 being, in turn, transmitted through the writing point of the tambour 

 to the kymograph. While it would be useless to compare the muscular 

 activity of two infants by comparing the excursions of the writing point 

 on the kymograph, nevertheless a general impression of the activity 

 and strength of an infant considered as a living mass of tissue may be 

 obtained by an inspection of these curves. 



Accompanying the curves are tables giving the simultaneous records 

 of the pulse-rate and the metabolism as computed on the basis of the 

 total heat output per 24 hours. An estimate of the activity is also 

 given in this table, using the basis of classification previously explained 

 in table 23. For convenience in referring to these estimates, the key 

 to the classification is given again here, being as follows: 



I. Very quiet, probably asleep. IV. Moderately active. 



II. Slight movements, few in number. V. Distinctly active. 



III. Some activity, but generally quiet. VI. Very active, most or all of the time. 



A comparison of the curves with this estimated activity will serve 

 to illustrate the method of estimation used in previous tables. 



Observation with J. V., February 27, 1913. 



The kymograph curve given in figure 43 was obtained with J. V. on February 

 27, 1913. This infant was very small and weak, weighing only 2.45 kilograms. 

 She was restless throughout the observation and no period can be classified as 

 activity I. As is usual with many of the observations, the preliminary period, 

 which began at 3 h 6 ra p. m., was characterized by considerable activity. At 

 3 h 34 m p. m. there was an ill-advised attempt to begin a new period, notwith- 



