1914] Lafayette B. Mendel 165 



perfect growth. At length nature waxing weaker, is not able to 

 restore and repaire so much as is wasted and decayed, whereby the 

 body beginneth to decrease, and the powers and strength thereof be 

 more and more diminished imtil such time as hfe, even as the Hght 

 of a lampe, be cleane extinguished. And this is called naturall 

 death, which few attaine unto, but are prevented by death casuall, 

 when by sicknesse or otherwise the said naturall moysture is over- 

 whelmed and suffocate. Now the meanes to preserve this naturall 

 moisture, & consequently to preserve life, is to use meates and 

 drinkes according to the age of the person. For the dyet of youth 

 is not convenient for old age, nor contrariwise." 



According to Minot, the more rapid growth depends upon the 

 youth of the individual — its small distance in time f rom its procrea- 

 tion. Cessation of growth is thus associated with age. We are 

 told that there is " a certain impulse given at the time of impregna- 

 tion which gradually fades out." The facts of regeneration in the 

 lower forms warn us, however, to be cautious in drawing conclu- 

 sions as to the loss of growth power. Something may inhibit it as 

 age progresses. It has even been alleged that growth is stopped 

 because an animal can digest only a limited quantity of food, and 

 that the adult size is the stage of equilibrium between the amount of 

 food digested and the amount used up. Experience in the field of 

 nutrition speaks against such an assumption. 



If we turn our attention to the unit of biological activity, the 

 cell, in seeking something more specific respecting the decline or 

 cessation of growth, certain general principles may be drawn into 

 consideration. In a unicellular organism under favorable condi- 

 tions of nutrition the process of building up exceeds the destructive 

 process so that the body increases in size up to a limit where fission 

 takes place. " What determines the limit is unknown, but the cause 

 is perhaps in some way connected with the geometric principle that 

 the volume of the cell increases as the cube of its diameter, whereas 

 the surface by which it absorbs nutriment and otherwise comes into 

 relations with the outside world increases only as the Square of its 

 diameter." Since activity is a function of the surface the larger the 

 unit the smaller must be its activity. An organism can only attain 

 a large size on this basis, by a multiplication of units, each present- 

 ing the same amount of surface as an individual cellular organism. 



