ACCELERATION OF RATE OF CELL DIVISION. 359 



an atmosphere of pure oxygen accelerates the development of the 

 eggs of Rana temporaries. He subjected eggs to oxygen, hydro- 

 gen, and to oxygen and carbon dioxide. The first one gave 

 marked evidence of acceleration, as follows (table from Jenkin- 

 son) : 



Hours. Oxygen. Controls. 



3 First furrow in some. No furrow. 



3^4 All but one with first furrow. Most with first furrow. 



4 All but one four cells. All with two cells. 



5 All with four cells. Most with two cells; a few with four. 

 47 Blastopore closed White hemisphere visible. 



73 Medullary fold. Blastopore closed. 



The experiments were carefully done so that matters of pres- 

 sure and other disturbing factors were controlled, and the results 

 may be attributed to the factor under consideration. The data 

 from the experiments with hydrogen seem less conclusive as to the 

 effects upon rate of cleavage, while no segmentations were obtained 

 in the carbon dioxide experiments. 



The effect of sodium hydrate upon Arbacia eggs was studied by 

 Loeb. He found that the development and growth can be accel- 

 erated if the solution be made weakly alkaline, the concentration 

 of sodium hydrate used being very small, perhaps .006 per cent, to 

 .008 per cent. Acids have only an inhibiting effect. The chief 

 cause for these effects must be that the oxidative processes in 

 living substance are favored by the weak alkali, while acids de- 

 crease the oxidative processes and thereby inhibit syntheses. 

 Loeb found that more than .2 cubic centimeter of i/io normal 

 NaOH would not go into solution in 100 c.c. of sea water, for 

 the amount of precipitate formed was only increased. Cleavage 

 in the alkaline solution was slightly accelerated, but the amount of 

 the increase was difficult to detect for any particular stage ; as 

 development progressed the effects became more clearly recog- 

 nizable, and by the time the swimming blastula stage is reached 

 the difference had become so pronounced that movement clearly 

 began earlier in the eggs in the alkaline solution. In one case 

 fertilization took place at 9:30 and at 3:15 the embryos in the 

 alkaline sea water were swimming in lively manner, while the 

 embryos in normal sea water remained motionless. In another 



