366 A. RICHARDS. 



it would seem, for the analysis of the forces and mechanism of 

 mitosis. 



SUMMARY. 



The list of agencies which have been previously found to accel- 

 erate the rate of cell division includes heat, x-rays, radium, thyroid 

 secretion, suprarenal extract, alcohol, dibasic potassium phosphate, 

 potassium sulphate, potassium bromide, oxygen, sodium hydroxide, 

 and pilocarpine hydrochlorate. 



The results of the experiments on the eggs of Haminea virescens 

 are in harmony with those of previous investigators. These ex- 

 periments show that the eggs may be induced to undergo cleavage 

 at an accelerated rate (although the amount of the acceleration 

 need not be great) by the following reagents : .004 per cent, to 

 .009 per cent. NaOH, .006 per cent, to .009 per cent. NH 4 OH, 

 .006 per cent, to .017 per cent. KOH, thyroid extract and pilo- 

 carpine hydrochlorate in weak concentrations. The accelerating 

 effect of the pilocarpine is less than that of the hydroxides men- 

 tioned. 



Barium hydroxide, chromium hydroxide, and pilocarpine nitrate 

 cause no acceleration. 



The experiments suggest that the hydroxides which are effective 

 in causing acceleration of cleavage are those of elements which 

 belong to the first group of the periodic series, and that those of 

 other groups are ineffective in these respects. 



Acceleration of cleavage is not always followed by continuously 

 quickened development, for in some cases the experimental eggs 

 do not hatch ahead of the control. The advantage gained in the 

 segmentation stages may later manifest itself in more vigorous 

 larvae rather than in more rapidly developing ones. 



The conclusion is also suggested that the agencies which are 

 capable of accelerating division bring about this result through 

 their property of influencing the enzymes of the cells, the setting 

 free and the activation of which are correlated with the mitotic 

 processes. 



BIBLIOGRAPHY. 



Budington, R. A., and Harvey, H. F. 



'15 Division Rate in Ciliate Protozoa as Influenced by Thyroid Constituents. 

 BIOL. BULL., 28. 



