338 



HUMAN PHYSIOLOGY 



the same build it will weigh about one-eighth as much, 

 while it will have one-fourth the surface of the larger 

 animal. Its metabolism under comparable conditions 

 will be nearer one-fourth than one-eighth that of the 

 rat. 



So a baby a year old and weighing 20 pounds will 

 probably have a metabolism of more than twice as 

 many Calories per unit of weight as that exhibited by 

 its parents. The rate will be fairly uniform for both 

 when it is referred to surface area. Such comparisons 

 are made at an external temperature high enough to 



a 



FIG. 68. If a cube measures twice as much as another along one of 

 its edges, it will have four times the surface and eight times the weight 

 of the smaller. The same principle must apply to two animals if they 

 are alike in build. 



avoid the reflex stimulation of the skeletal muscles to 

 which we have alluded. The area of the full-grown 

 human body has been estimated at 1.7 square meters, 

 and as the minimum metabolism is somewhat less than 

 2000 Calories the standard quantity per square meter 

 appears to be about 1000, a convenient round number. 1 

 It does not vary much from this in several very unlike 

 species of animals of the " warm-blooded " order. 



Students are likely to question whether mental exer- 

 tion noticeably increases the metabolism. Careful ob- 



1 According to certain authorities the surface is greater, about 2 

 square meters. This gives a daily value per square meter of 800 

 Calories or a little more. 



