30 THE UNIVERSITY OF OKLAHOMA 



of any harmful agency is to depress the rate of development. But 

 in many of these cases the effect is doubtless upon the entire 

 organism rather than upon the mitotic mechanism, so they do not 

 give much insight into the nature of the processes. 



A more productive means of analysis of the mechanism comes 

 from the study of the agencies which may be used to accelerate the 

 division rate, for these agencies must operate upon the mechanism 

 of mitosis itself. 



Although the problems of growth have long been studied, not 

 many agencies have been found which will shorten the time of 

 mitosis. The list of which the writer has found published record 

 is as follows : heat, x-rays, radium, thyroid secretion, supra-renal 

 extract, alcohol, dibasic potassium phosphate, potassium sulphate, 

 potassium bromide, oxygen, sodium hydroxide, and pilocarpine hydro- 

 chlorate. Of these, x-rays, radium, and thyroid are the most 

 marked in their effcts. All of these agencis are able more or 

 less effectively to increase the rate of cell division. In those cases 

 where the effect is slight, the results are still significant because 

 they are constant. The careful analysis of any constant increase 

 in the rate of division should throw new light upon the forces by 

 which the divisions are produced. 



Expirements 



During the summer of 1921 while working at the Laboratory of 

 the Scripps Institution for Biological Research at La Jolla, Cali- 

 fornia, the writer attempted to verify some of the agencies listed 

 above and to extend the investigation to others. For this purpose 

 the eggs of the gasteropod, Haminea z'iresccns (Sby) were used. 

 These eggs as the writer has shown in another paper, are especially 

 useful for experiments in which the effect of a particular reagent 

 is sought while the environment of the developing egg is partically 

 unchanged except in regard to the factor in question. They are 

 laid in a complicated manner in a jelly-like ribbon in which all are 

 in the same stage of development. This makes is possible to cut 

 up the ribbon into strips using one for a control and others for 

 experiments as seems desirable. One has merely to place some of 

 the pieces in sea water for a control and others in sea water con- 

 taining the reagent whose properties are being investigated, to have 

 a complete experiment. 



The first experiments were with sodium hydroxide following 

 Loeb's observations on Arhacia. Haminea eggs are slightly accel- 

 erated in cleavage by solutions containing .004% to .009% NaOH. 

 But the accelerations of cleavage does not always result in the 

 earlier hatching of the experimental eggs, for in some cases the 



