GROWTH AND THE AGING PROCESS 



969 



and Hoelzel (1946), Templelon and Ershoff (1949) and McCay (1942) for rats. 



The relation of regeneration, the replacement of lost parts or even of very large 



portions of the body, to the process of senescence also has been investigated. The 



great work of Child many years ago (191 5) had pointed out the rejuvenative 



Fig. II. Amitotic division of the nucleus in an old specimen of the protozoan Tokophyra 

 infusionum. X 1692. (Courtesy of Dr. M. A. Rudzinska). 



effects on the organism of the stimulus to regeneration. Sonneborn (1930) showed 

 that in the worm Stenostomum there is a distinct difference in the fate of lines 

 which are maintained from the anterior half of the worms and from the posterior 

 halves. Those from the posterior halves, where there is need for a great deal of 

 regeneration and differentiation, continue to remain vigorous. Those from the 

 anterior halves, where there is need for relatively little regeneration, soon "age" 

 and die out. Indeed, the lines arising by regeneration from the posterior halves 

 may be said to be essentially immortal ! Again we see the close relation between the 

 processes of growth, "regeneration" in this instance, and of senescence. 



CONCLUSION 



In its broad sense, taken to mean an increase in living matter, growth probably 

 lasts as long as life ; that is, there are some parts of the organism, some cells through- 

 out the body, which are building up new protoplasm even though the organism as 



Literature p. gji 



