CELL DIVISION — SPINDLE IN SEA-URCHIN EGGS 213 



The centrifuge used was a Bausch & Lomb hand centrifuge, 

 equipped with two speeds. In the following experiments, how- 

 ever, the high speed was always employed. This necessitated a 

 use of the hematocrit attachment, the eggs being placed in small 

 glass tubes. Because of the difficulty with which such small 

 tubes are cleaned, it was found advisable to use new tubes for 

 each centrifuge test. A pair of tubes can be made in less time 

 than it takes to thoroughly cleanse them. 



In comparing the viscosity of eggs at one stage with the vis- 

 cosity at a later stage, two methods of procedure are possible. 

 In the first place, the eggs can be fertilized at two different times, 

 and then eggs from both lots centrifuged simultaneously. In this 

 way, the experimenter can assure the same treatment to both 

 sets of eggs. Earlier tests were made in this way, and it was 

 possible to demonstrate that after fertilization the egg viscosity 

 first increased and then decreased. But a closer study of the 

 process demanded viscosity tests at frequent intervals. In order 

 to accomplish this conveniently, only a single lot of eggs can be 

 studied. The experimenter must therefore learn to handle the 

 centrifuge with such precision that the centrifugal force gener- 

 ated in each of the tests is constant. The handle of the centri- 

 fuge has to be turned a certain number of times in a certain num- 

 ber of seconds, and great care must be taken that the turning is 

 uniform, for the centrifugal force of course depends on the speed. 

 With a little practice, one may acquire the knack of turning the 

 handle with machine-like precision. 



In the accompanying tables, the amount of centrifugal force 



exerted on the eggs is given precisely by recording the number 



of times the handle was turned in a certain time interval. Each 



turn of the handle resulted in 130 revolutions of the tubes. The 



distance between the ends of the tubes was 12 cm. The centrifu- 



mv^ 

 gal force is given by the formula C = . In this formula, 



the mass m is unknown, but presumably constant, the velocity 

 V = 2-Kr X the number of turns per second, r the radius is always 6. 

 Thus, when the handle is turned at different speeds, the amount 

 of centrifugal force generated varies directly as the square of the 

 number of turns per second. 



