THEORETICAL CONSIDERATIONS 2^1 



same story of multiplicity of factors and complexity of function. 

 Therefore, with reference to the influence of radium rays, we must 

 consider as many possibilities as there are steps and combinations of 

 steps. First and foremost we must take into account the living sub- 

 stance itself. Then the rays may affect the enzymotic digestion of 

 the food, partly outside and partly inside of the cells to be nourished. 

 Furthermore the rays may operate so as to increase or decrease the 

 amount of energy available for the work, and, lastly, variations in 

 growth may be, either wholly or partly, expressions of the influence 

 of the rays on cell-division. 



Cell-division : No one has yet succeeded in accelerating the 

 rate of cell-division or in increasing its amount in a given tissue by 

 means of radium rays. The only results recorded are the introduction 

 of irregularities and complete inhibition. A brief resume of the 

 well known life-history of a cell may serve as the first step in attempt- 

 ing to explain this effect. 



On the basis of Verworn's theory, the active metabolism of a 

 young cell involves, fundamentally, the continual destruction and 

 reconstruction of biogen molecules. The latter process is condi- 

 tioned, in part, by the supply of suitable food material, and upon 

 its preponderance over the breaking down of the biogens depends 

 the growth of the cell. With cell-enlargement by growth the area 

 of the cell-surface in proportion to the mass becomes finally too 

 small to permit of the entrance of enough food and energy to 

 maintain the reconstruction of the biogen molecules faster than 

 they are decomposed. If the surface area relative to the mass can 

 be increased, rejuvenescence will result, but otherwise the biogen 

 molecules will continue to break down faster than they can be built 

 up again, and the cell enters upon a period of senescence. In grow- 

 ing old either certain catabolic products are produced in relatively 

 larger quantities than occurs in the pre-senescent period, or new cata- 

 bolic substances are elaborated, or both. Normally cell-division 

 postpones the approach of senescence.* 



The evidence at hand, and presented in Chapter XVI, indicates 

 that radium rays may hasten the approach of senescence. In other 

 words, they may accelerate the breaking down of biogen molecules and 

 interfere with their reconstruction. This is doubtless accomplished by 



* Of course cell-division cannot indefinitely postpone senescence, nor are the above 

 circumstances regarded as the only condition or stimulus of cell-division. 



