EQUIVALENT AGES 



133 



are lighter: — the most striking differences from the computed 

 values being shown by the heavier thyroid, brain and lungs, and 

 the lighter eyes. While the differences thus revealed are of 



TABLE h9 

 Percentage weight of systems in man and albino rat 



interest, the greater significance is to be attached to the general 

 similarities of the two forms. 



Equivalent ages. It has already been stated that post natal 

 growth of the rat is about thirty times as rapid as that of man, 



TABLE 90 

 Weights of the organs in the rat compired with man 



Liver 



Kidneys (2) . . . . 



Heart 



Spleen 



Thyroid 



Suprarenals (2) 



Lungs 



Eyes 



Brain 



R.^T 300 GRAMS, 

 MALE 



COMPUTED FOR 



MAN 65 KILOS, 



MALE 



grams 



13.7 

 2.5 

 1.1 



0.79 



X 217 

 X 217 



217 

 217 



0.044 X 217 

 0.045 X 217 



1.7 



0.33 



2.00 



X 217 



X 217 

 X 217 



2972.9 



542.5 



238.7 



171.4 



9.5 



9.8 



368.9 



71.6 



434.0 



OBSERVED 

 MAN 



grams 



1800 



400 



350 



220 



35 



74 



995 



13.5 

 1430 



Hoffman 



Hoffman 



Hoffman 



Hoffman 



Piersol 



Vierordt 



Vierordt 



Vierordt 



Vierordt 



and it is conspicuously true that in the growing nervous system 

 the degree of development attained in the rat at a given age is also 

 attained by man when thirty times as old. 



In the span of life, however, some of the major events are 

 differentl}^ spaced. Thus suckling continues in the rat for 20-25 



