IVOR CORNMAN 143 



at 21 °C, 17% at 17° and was partially suppressed at 13° in one series using 

 55 niM urethan. In another, 44 mM retarded 2% at 21°, 7% at 25° and 27% 

 at 29°. Ethyl-N,N-diethyl carbamate also retarded minimally at 20°-21°. 

 It was always more effective than urethan, 7 mM retarding first cleavage 

 10% at 21°. Echinarachnius also showed these two separate trends in re- 

 sponse to temperature, but the break in the curve came at 16°. It is pro- 

 posed that the carbamate series are typical nonspecific hypnotics, held 

 loosely in the cell by some physical mechanism. The carbamate molecules 

 are less readily captured by the cell components at higher temperatures, 

 but beyond a critical temperature, heat accelerates the process promoted by 

 the carbamates. Denaturation of a single enzyme would fit this picture, 

 but the system is too complex to yield a definitive answer on the basis of 

 the evidence at hand. 



REFERENCES 



1. CoRNMAN, I. Inhibition of sea-urchin egg cleavage by a series of .suljstituted car- 

 bamates. J. Nat. Cancer Inst. 10: 1123-1138, 1950. 



2. CoRXM.^N, I. The properties of urethan considered in rehition to its action on 

 mitosis. Internat. Rev. Cytol. 3: 113-130, 1954. 



3. CoRNMAN, I., H. E. .Skipper and J. H. Mitchell. The fixation of urethan carbon 

 atoms in si)erm and in resting and rapidly dividing cells. Cancer Res. 11: 195-199, 

 1951. 



4. Harvey, Ethel B. Tlie American Arbacia and Other Sea Urchins. Princeton, N. J.: 

 Princeton, 1956. 



5. Johnson, F. H., H. Eyring and M. J. Polissar. The Kinetic Basis of Molecular 

 Biology. New York: Wiley, 1954. 



