DISCUSSION OF RESULTS. 141 



dioxide output per hour was 4.50 grams. In the next two periods, 

 the pulse-rates were 112 and 113 respectively and the carbon-dioxide 

 production 4.82 grams and 4.84 grams respectively, showing the usual 

 harmony. 



This evidence of the relationship between the pulse-rate and the 

 metabolism, taken in connection with the evidence presented in previous 

 sections of this book, gives an entirely new significance to the pulse- 

 rate, since it may be considered as a very fair index of the metabolism. 

 In other words, an infant having a pulse-rate of 120 at one period of 

 the day and of 150 at another period has unquestionably a greater 

 metabolism in the second period. There is no evidence, however, that 

 a difference in the pulse-rate of any two infants necessarily indicates 

 a proportional difference in the metabolism, even though the infants 

 be of the same weight and age, and the periods of observation of the 

 same length. But it is safe to say that variations in the pulse-rate 

 of an infant indicate a similar change in the metabolism. 



It is not to be inferred that we believe that the increase in metabolism 

 noted with increased pulse-rate is due exclusively to the mere mechan- 

 ical work of circulation, as this is far from our belief. We especially 

 wish to emphasize the fact that we look upon pulse-rate as an index 

 of muscle or general tonus in the body and not as referring solely to 

 the work of the heart muscles. 



We may state, therefore, that whatever increases the pulse-rate also 

 increases the katabolism, so that when the pulse-rate is elevated by 

 the muscular activity incidental to restlessness, playfulness, laughing, 

 or crying, or pathologically as in fever, we have every evidence that 

 the katabolism is likewise increased and a larger proportion of food 

 material or body substance is being consumed. 



BASAL METABOLISM OF INFANTS STUDIED. 



In beginning this research upon infant metabolism, one of the funda- 

 mental questions which presented itself to us with special force was 

 as to what may be considered the normal basal metabolism of infants. 

 Consequently we made it our aim to study as many infants as possible 

 and to secure a sufficient number of periods of complete repose on a 

 sufficient number of days to establish beyond reasonable doubt the 

 basal metabolism of each infant. The infants secured for these obser- 

 vations varied sufficiently in age, weight, height, and sex to permit 

 a comparative study of the results as to the constancy or lack of con- 

 stancy in the metabolism. 



