THE ACCELERATION OF THE RATE OF CELL DIVISION

The list of agencies which have been previously found to accelerate 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 hydrochiorate.

The results of the experiments on the eggs of Haminea virescens are in harmony with those of previous investigators. These experiments 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. NH₄OH, .006 per cent. to .017 per cent. KOH, thyroid extract and pilocarpine hydrochlorate in weak concentrations. The accelerating effect of the pilocarpine is less than that of the hydroxides mentioned.

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 larvæ 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.