The Mechanics of Mitosis 33 



some of 2 cm. per second. It is, of course, almost impossible to 

 say what effect a viscous, heterogeneous field would have upon the 

 calculation, so we are obliged to leave the quantitative side of the 

 question as quite unsettled. 



Besides the oscillatory currents produced by pulsating and oscil- 

 lating bodies, Bjerknes has shown the existence of steady currents 

 in the fluid medium toward and away from the centers of motion. 

 Similar currents have been observed in dividing cells, particularly 

 centripetal currents between the astral centers. It does not, how- 

 ever, seem wise to treat this or similarly less pronounced phe- 

 nomena in our present state of ignorance. 



The assumption of a pulsating centrosome or centrosphere is by 

 no means an impossible one. The assumption of an oscillating 

 centrosome is not even improbable. The assumption of syn- 

 chronous pulsations or oscillations involves no mysterious synchro- 

 nizing mechanism. Random oscillations or pulsations would cer- 

 tainly tend to become synchronous by mutual interaction, while 

 after the closed spindle fibers had formed, whatever their nature 

 may be, any other rate of oscillation would be very improbable. 



The fact that such oscillation or pulsation have not been de- 

 scribed is not conclusive. 



Our knowledge of the subject is based almost wholly on dead 

 material, and moreover the oscillations and pulsations may be 

 very rapid and small. 



In conclusion, I would again like to emphasize that the above is 

 nothing but an ad hoc constructed hypothesis and intrinsically 

 therefore only of hypothetical value. If, however, it calls atten- 

 tion to a little known phenomenon or stimulates fresh observation 

 it will have served its purpose. 



