author's abstract of this paper issued 



Br the bibliographic service, DECEMBER 29 



AN EXPERIMENTAL STUDY OF CELL-DIVISION 



I. THE PHYSICAL CONDITIONS WHICH DETERMINE THE APPEARANCE 

 OF THE SPINDLE IN SEA-URCHIN EGGS 



L. V. HEILBRUNN 



University of Michigan 



INTRODUCTION 



In my work on artificial parthenogenesis, I showed that all 

 substances which incite the sea-urchin egg to divide mitotically 

 produce a marked increase in the viscosity of the cytoplasm. A 

 similar viscosity increase was also found to occur after the nor- 

 mal stimulus of fertilization. Accordingly, I held the view that 

 some sort of 'solidification' was the essential factor which initi- 

 ated mitosis. For purposes of clearness, I shall refer to this stif- 

 fening as a gelation. In order to prove my view correct, I have 

 now attempted to show that if this gelation is prevented, no stim- 

 ulus to mitosis can occur. If the cytoplasm of a fertilized egg 

 is kept in the fluid condition, then no mitotic figure forms, and 

 the egg remains undivided, although it is not necessarily injured 

 by the treatment. Here, then, is additional evidence in favor of 

 the view that the formation of the amphiaster is a direct con- 

 sequence of cytopla.smic gelation. 



It can readily be seen that such a study of mitosis leads in two 

 directions. In the first place, it throws light on the genesis of 

 the mitotic figure; secondly, it affords a physical interpretation of 

 stimulation and anesthesia in the egg. In this contribution I 

 propose to emphasize the first of these problems, reserving the 

 discussion of anesthesia for a later paper. 



The experimental work which furnishes the basis for this paper 

 was done at Woods Hole during the summer of 1916. The form 

 used was Arbacia punctulata (Gray). 



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the journal of experimental zoology, vol. 30, NO. 2 



