xii INTRODUCTORY LETTER TO SENATOR MOSSO 



delightful student days have brought many changes, 

 and have transformed us into members of the older 

 generation. Therefore, I hope that you will regard 

 the dedication of this volume on age to yourself as not 

 inappropriate. As I write I recall our parting in the 

 forest of Fontainebleau, our meeting on the glacier 

 above Zermatt, our paddling together in a canoe on 

 an American lake along the edge of the primeval 

 forest, and many other experiences which we have 

 shared. These were in our younger days, and now 

 our interest in what is essential among the effects of 

 age has a personal as well as a scientific foundation. 



This book deals with a series of important biologi- 

 cal problems, yet it is essentially a study of a single 

 phenomenon, the increase in the amount of proto- 

 plasm. The increase to be considered is not that 

 which takes place at large in the body of the growing 

 animal, but that which takes place within the limits of 

 single cells, and occurs in such a manner that the 

 proportion between the cell-body and the nucleus in 

 volume, or bulk, is changed the cell-body becoming 

 relatively either larger as more frequently happens, or 

 smaller, as happens in special cases. 



By the study of the proportionate volumes of the 

 nucleus and the cell-body we can demonstrate, I be- 

 lieve, certain laws governing that proportion, and 

 prove that the variations of the proportion establish 

 conditions which are fundamental to the correct con- 

 ception of the problems of growth, differentiation, 

 death, and sex. It is my endeavour, by following the 



