140 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



lute time and percentagewise: 6% and 12% for first and second cleavages 

 at 20.6°C and 20% and 19% for the cleavages at 16.6°C. Further cooling 

 made urethan even more effective, but extending the temperature above 

 20°-21° also increased the efficiency of urethan. From this it was concluded 

 that around 20°-21°C, the cells were minimally susceptible to urethan. 



Before generalizing, we must ask whether other carbamates imitate this 

 urethan response to temperature as well as they do the cytological altera- 

 tions. Comparison was limited to one carbamate with a completely sub- 

 stituted nitrogen: ethyl-N,N-diethyl carbamate. Figure 3 shows curves 



140 160 



I I 



MIN AFTER PERT 



29.2* C 



CONTROL 



o -e 



,NCOOC H 



Fig. 3. Retardation and abor- 

 tion of Arbacia cleavage by 6.6 

 mM diethyl urethan. At 12.6°C, 

 80% of the eggs formed deep 

 temporary furrows that subse- 

 quently regressed. Successful 

 50% cleavage was delayed 64% 

 beyond control cleavage at 12.6° 

 and 127% beyond the controls 

 at 29.2°C. 



310 



from two experiments. Simultaneously with the curves at the top, eggs 

 were exposed at 25.2° and 21.2°. At 21° the retardation of first cleavage 

 was 6V2 minutes and second cleavage 11 minutes beyond the control 50% 

 cleavage times of 60 minutes and 94 minutes. At 25° the retardation was 

 13 minutes for first cleavage and 18 minutes for second cleavage, com- 

 pared to control 50% cleavages at 45 minutes and 69 minutes. Percentage- 

 wise, first cleavage delay was 11% at 21°, 29% at 25° and 127% at 29°. 

 The curves at the bottom of the figure represent the coldest of a series that 

 included 16.6° and 20.6°. In this series, delay by 0.1% diethyl urethan was 

 about equal at 16.6° and 20.6°: 4 minutes ait first cleavage and 10 to 12 

 at second. Percentage delay of first cleavage was 6% at 20.6°, 6% at 16.6° 



