VI 



THE FOUR LAWS OF AGE 



J^ADIES AND GENTLEMEN: I have re- 

 ferred in these lectures repeatedly to the cell 

 and its two component parts, the nucleus and the 

 protoplasm. To-night I shall have only a few refer- 

 ences to make directly to these, and shall pass on for 

 the latter part of the hour to another class of con- 

 siderations bearing upon the problem of age. Before 

 we turn to these new considerations, however, I wish 

 to say a few words by way of recapitulation concern- 

 ing the changes in the cells as corresponding to age. 

 Cells, as you know from what I have told you, un- 

 dergo in the body for the greater part a progressive 

 change which we call their differentiation. We may 

 say that there are four kinds of cells for purposes of 

 an elementary classification to be used in a simple ex- 

 position like the present. The first kind are those 

 cells of the young type, in which the protoplasm is 

 simple, and shows as yet no trace of differentiation. 

 These cells are capable of rapid multiplication, and 

 some of them are found still persisting in various 

 parts of the adult body, and serve to maintain the 

 growth of the body in its mature stage. Another 



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