470 



L. V. HEILBRUNN. 



When (unfertilized) sea-urchin eggs are placed in 2^ per cent, 

 or 3 per cent ether, there is, within a few minutes, a very pro- 

 nounced decrease in viscosity as shown by tests with the centrif- 

 uge. In the following table the viscosity of etherized and normal 

 control eggs is compared. The viscosity numbers represent the 

 number of seconds of centrifugal treatment necessary to produce 

 a given degree of granular movement. Usually the eggs were 

 centrifuged until the clear hyaline zone extended along one third 

 or one half of the axis of the egg. Naturally a number of tests 

 had to be performed to obtain any given value. The centrifugal 

 force employed was approximately 4,968 times gravity and the 

 centrifuge used was an ordinary hand centrifuge with haematocrit 

 attachment. Details of technique are given in earlier papers 

 (16, 22). Because of the fact that a series of tests had to be 

 performed for each value of the viscosity and because moreover 

 the viscosity of the etherized protoplasm is not constant, the 

 tests had to be made hurriedly. They are not extremely accu- 

 rate, and it is entirely possible that the inaccuracy amounts to 

 10 or 20 per cent. The decided difference between unetherized 

 and etherized eggs makes this inaccuracy of small consequence. 

 In the table the first column gives the percentage of ether used 

 (volume per cent, in sea- water). The second column represents 

 the time of exposure to ether, that is to say the number of 

 minutes elapsed after immersion in ether solution at the time 

 the critical test was made. The third column gives the relative 

 viscosity of the etherized eggs as compared to that of the normal 

 control eggs shown in the fourth column. The temperature of 

 the experiments varied from 22 to 25 degrees. It is given in the 

 fifth column. 



Averaging the above values it is seen that in 2^2 per cent. 



