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 89 



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 



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 tunes as old. 



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

 differently spaced. Thus suckling continues in the rat for 20-25 



