ACCELERATION OF RATE OF CELL DIVISION. 365 



If the list of hydroxides which cause acceleration be inspected, 

 it is noted that they are the hydroxides of elements which belong 

 to the first group of the periodic series (with the exception of 

 ammonium, which, however, behaves chemically as do the members 

 of that group). It is to be noted also that the hydroxides of 

 barium of the second group and of chromium of the sixth group 

 fail to induce the acceleration. One may suppose that it is only 

 hydroxides of the first group that are effective in causing accelera- 

 tion. This tentative conclusion is the object of certain experi- 

 ments now being carried on, which at the date of the writing seem 

 to bear it out. It is true that only hydroxides of the first group 

 have any high degree of solubility, but this is discounted by the 

 fact that the amount of any hydroxide which will go into solution 

 in the already slightly alkaline sea water without causing precipita- 

 tion is very small. 



These results, I think, throw light upon the nature of the mitotic 

 process and upon the mechanism by which it is accomplished. 

 Practically all of the means now at our disposal for accelerating 

 the rate of mitotic divisions are in line with increased oxidations 

 and increased metabolism of the cells. Furthermore, a number of 

 these accelerating agents are already known to affect favorably 

 enzymatic activity. For example, the radium and x-ray studies 

 previously referred to indicate that the accelerating and retarding 

 effects of radiation are produced upon the enzymes of the cells. 

 In this connection it is to be recalled that Mathews and others have 

 suggested that the mitotic processes are correlated with the setting 

 free and the activation of intracellular enzymes. The changes in 

 the rate of enzyme action are able to bring about changes in the 

 rate of division ; and since the radiations affect the enzymatic 

 activity, it is to be supposed that the changes which they induce in 

 the rate of division are to be accounted for on the basis of this 

 chemical mechanism. These considerations lead the writer to sug- 

 gest that the agents which have been shown (either in this paper 

 or in the list on a preceding page) to be capable of accelerating 

 division do so because they possess the property of activating, 

 either directly or indirectly, the inactive enzymes of the cells, or 

 by increasing the activity of those which have already been acti- 

 vated. This line of approach offers a most profitable opportunity, 



