ACCELERATION OF RATE OF CELL DIVISION. 



363 



Potassium hydroxide is also similar in its effect, but the eggs 

 respond with the more rapid division rate only to a slightly stronger 

 concentration than in the case of NaOH. Experiment 161 fur- 

 nishes an example of the KOH effects. 



EXPERIMENT No. 161, AUGUST 2, 1921. BEGAN AT 7:00 A.M. EGGS IN 4-CELL 



STAGE. 



8/8 7:00 A. M. 



161.1 24 hatched. 



161.2 2/3 hatched. 



161.3 9/10 hatched. 



161.4 A few hatched. 



161.5 All hatched. 



8/96:45 A. M. 



all hatched. 



8/10 hatched. 



all hatched. 



never hatched. 



It was desired by the writer to try the effect of various other 

 hydroxides, especially those belonging to the first periodic group; 

 but in the time at his disposal for the experiments he was able to 

 obtain only two others, namely, barium hydroxide, Ba(OH),, and 

 chromium hydroxide, Cr 2 (OH) 3 . Eggs were placed in solutions 

 containing, respectively, .005 per cent., .006 per cent., .009 per 

 cent., and .01 per cent, of barium hydroxide. In one experiment 

 it seemed that some slight acceleration of the cleavage rate was 

 probably affected by the reagent, but it was not possible after- 

 wards to repeat that result and the writer is therefore disposed to 

 believe that some other factor must have been responsible for the 

 response observed. With chromium hydroxide also no accelera- 

 tion could be seen in the cleavage rate. 



Several experiments upon the effect of thyroid extract upon the 

 cleavage rate were tried. A preparation of Parke Davis's desic- 

 cated thyroid was tried, with somewhat varying results. .The 

 experiments justify the statement that thyroid contains some agent 

 which is able to increase at least slightly the rate of cleavage in 



