Twentieth meeting. 



Rockefeller Institute for Medical Research. February 20 , igoy. 

 President Flexner in the chair. 



26 (169) 



Experimental studies on nuclear and cell division. 

 By EDWIN G. CONKLIN. 



[From the Zoological Laboratory, University of Pennsylvania^ 



During several seasons extensive experiments were made on 

 the segmenting eggs of Crepidula plana. These experiments 

 included a study of the influence on nuclear and cell division of 

 hypertonic and hypotonic sea water, of ether, alcohol, etc., of the 

 lack of oxygen, of the electric current, and of pressure and shak- 

 ing. The following general conclusions may be drawn from this 

 work : 



1. Under the same treatment the effects may be extremely 

 varied, owing, probably, to the different stages of cell division 

 acted upon. 



2. A dividing cell is much more easily disturbed or rendered 

 abnormal than is a resting one ; the mitotic figure in particular is 

 very easily altered and most of the abnormalities observed arise 

 from this source. 



3. The earlier stages of cleavage are much more easily altered 

 than are the later ones. 



4. Certain general abnormalities occur after the most varied 

 treatment, e. g., the general results both of concentration and of 

 dilution of sea water are to produce polyasters and to prevent the 

 cleavage of the yolk. 



5. On the whole the results of the hypertonic solutions are the 

 same whether they are produced by evaporation of the sea water 

 or by the addition of NaCl, MgCl 2 , or KC1 to sea water ; in short, 

 these salts exert no specific action on cell division. 



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