232 L. V. HEILBRUNN 



tube tightly sealed with a rubber stopper, and the test-tube was 

 then exposed to a temperature which varied from 10° to 12°. 

 No spindle appeared while the eggs were in the cold, but when 

 the test-tube was removed from the cold after an exposure of 

 two hours and thirty-eight minutes and warmed with the hand, 

 then spindles soon made their appearance. Thirteen minutes 

 later they could be observed plainly. During their two and one- 

 half hours' stay in the cold, the eggs must have been thoroughly 

 penetrated by the KCN solution, and yet as soon as they were 

 placed in a warmer temperature, development proceeded as far 

 as the spindle stage. Of course no segmentation occurred in 

 these eggs. 



The following experiment shows that in a 0.005 per cent solu- 

 tion of KCN, the final stages of mitosis can proceed: 



August 23rd. Some eggs were fertilized at 8:23 p.m. and they first 

 began to segment forty-two minutes later. At 30, 33, 35, 38, 40, 42 

 minutes after fertilization these eggs were removed to stoppered test- 

 tubes A, B, C, D, E, F, respectively, each of which contained 0.004 per 

 cent KCN in sea-water. Counts of the segmenting eggs showed in F, 

 tV«; in E, ^%%-; in D, tm; in C, x^'^o-; in B, yV,,; in A, foV; normal con- 

 trol eggs, 1%. In these fractions the numerator represents the num- 

 ber of segmenting eggs counted, the denominator, the total number of 

 eggs observed. Thus it is apparent that for the last twelve minutes the 

 cleavage process is able to continue in the presence of 0.004 per cent 

 KCN. 



In order to explain this curious action of KCN on one particu- 

 lar stage of mitosis, I have already suggested that the cyanide 

 renders irreversible the normal gelation. Even before the above 

 experiments were performed, I had evidence supporting this view. 



June 25th. Some eggs fertihzed at 2:54 p.m. were at 3:14 p.m. sub- 

 jected to the action of 0.005 per cent and 0.0025 per cent KCN. At 

 3:34 p.m. eggs in 0.005 per cent KCN were centrifuged simultaneously 

 with normal eggs, the handle of the centrifuge being turned 45 times in 

 30 seconds. The eggs exposed to the cyanide showed no stratification 

 whatsoever, whereas the normal eggs, as expected, showed a very dis- 

 tinct stratification. A later test of the eggs in 0.0025 per cent KCN 

 gave similar results. Thus the KCN prevents the normal reversal of 

 gelation. 



