6 4 



THE EVOLUTION OF_J1EATH 



of temperature, which is known to have a great influence upon 

 growth. Nature makes this exclusion for us in the case of 

 warm-blooded animals. I selected for my own experiments on 

 warm-blooded animals guinea pigs for various practical reason 

 and I maintained a colony of these animals for many years. 

 Every animal of the colony was weighed at definite intervals of 

 age. After many thousands of determinations of the weight 



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wnj/i 

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50- 



FIG. 26. Graphic representation of the increase of weight in children of the Boston 



schools. After H. P. Bowditch. 

 (Knaben, boys. Madchen, girls. Jahre, years.) 



had been collected, they were worked over statistically. 33 

 My first problem was to invent a method which permitted 

 the representation of the rate of growth. Formerly investi- 

 gators were satisfied to represent growth graphically in a very 

 simple way. Curves were constructed in which the abscissae 

 corresponded to the age, and the ordinates to the weight, 

 Fig. 26. Such a curve, however, although it represents the 



