CYTOMORPHOSIS 



33 



fi 



have discussed more fully the alterations of the rapidity of 

 growth with age and its relation to the increase of difif erentia- 

 tion. The development of a mammal begins with an extra 

 power of growth. How gradual the increase is it is not yet 

 possible to determine exactly, but certainly the original daily 

 increase is not less than looo per cent. This holds true for 

 man also. 



Immediately after birth one finds the highest rapidity in 

 the rabbit to be not quite i8 per cent, per day; in the chick 

 not quite 9, and in the schs.l 



guinea pig about 51/2 per 

 cent. The relations for 

 man are similar. It is 

 therefore clear that the 

 animals mentioned and 

 man also have lost at the 

 time of their birth 99 per 

 cent, of their original 

 growth capacity. In fact, 

 from the biological stand- 

 point we are really old by 

 the time we are born and 

 the alterations which make 

 us old have for the most 

 part already occurred. The further losses which we suffer 

 from birth to old age are comparatively small, and we live 

 long only because these losses take place slowly. If the 

 progress of alteration after birth should be even only 

 approximately as swift as before birth we should live only 

 a very short time. And in fact the microscope shows us 

 that the multipKcation of cells after birth is by no means so 

 great as before, and that it goes on slowly. 



ke 

 Fig. 20. — Cell from the pancreas of the 

 larva of Salamandra maculosa, sec. h, 

 sec. k', secretory granules; x, formative 

 focus of the same; fi, secretory fibrils; ke, 

 nucleus; schs. i, closing plate. — After K. C. 

 Schneider. 



