168 GASEOUS METABOLISM OF INFANTS. 



the older under-nourished infants, is highly probable and we find 

 ourselves thoroughly convinced that the metabolism is determined 

 not by the body-surface but by the active mass of protoplasmic tissue. 

 With normal infants of varying weights, it is quite probable that the 

 active mass of protoplasmic tissue varies directly with the age. Since 

 it has been shown that not only body-surface but more recently that 

 the blood-volume, the size of the aorta, and the size of the trachea 

 with several species of mammals bear a direct relationship to the cube 

 root of the square of the body-weight, 1 it is not surprising that most 

 experimenters have observed that with adults the metabolism is roughly 

 proportional to the body-surface. If the blood-volume and the area 

 of the trachea and the aorta are proportional to the cube root of the 

 square of the body-weight, it is reasonable to suppose that the active 

 mass of protoplasmic tissue may develop normally on this ratio. When 

 there are marked variations from the average, as with excessive or with 

 deficient adipose tissue, this relationship can not be expected to hold. 



If, therefore, it is maintained that the total metabolism is propor- 

 tional to the body-surface, it should be stated that this is not due to 

 the fact that there is a loss of heat from the body-surface and that 

 Newton's law of cooling determines the intensity of the metabolism, 

 but that with normal individuals the body-surface, blood-volume, the 

 area of the trachea and the aorta, and probably the active mass of 

 protoplasmic tissue, are all in simple mathematical relation to the 

 body- weight. Thus the apparent relationship which has previously been 

 observed between the heat-output and the body-surface with normal or 

 nearly normal individuals has an explanation in that with such individ- 

 uals a simple relation exists between the body-surface, blood-volume, 

 body-weight, and the mass of active protoplasmic tissue. 



In our series of observations we have attempted to eliminate com- 

 pletely all muscular activity, to make the experiments under approxi- 

 mately the same conditions as to nutriment, to select such a diet as 

 was least stimulating to the katabolism, and to have our subject for 

 the most part in deep sleep, thus eliminating psychic disturbances. 

 With these conditions we hoped to obtain the fundamental minimum 

 metabolism, upon which we might base our discussion. 



The basal metabolism as we have outlined above, can not in any 

 wise be considered a direct function of the body-weight and the body- 

 surface, and particularly has no relationship with body-surface on the 

 basis of the law of cooling bodies. 



We believe that our evidence points strongly and conclusively to 

 the fact that the active mass of protoplasmic tissue determines the 

 fundamental metabolism. The absence as yet of a direct mathematical 

 measure of the proportion of active protoplasmic tissue does not, we 

 believe, in any wise affect the convincing nature of our evidence. 



x Dreyer and Ray, Phil. Trans., 1909-1910, 201, ser. B, p. 133; Dreyer, Ray, and Walker, 

 Proc. Roy. Soc, 1912-1913, 86, ser. B, pp. 39 and 56. 



