138 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



egg. Then the delayed first cleavage and the second cleavage progress al- 

 most simultaneously. There is more than coincidence in this. It reflects a 

 fundamental relationship between the achromatic figure and cytoplasmic 

 cleavage. One can observe in these eggs, coincident with the postponement 

 of cleavage, a mitotic figure smaller than normal. It is reasonable to sup- 

 pose that during the first mitotic cycle the division figure was too weak 

 to divide the cytoplasm completely. The nuclear cycle continued, however, 



lOOp 



n 



MIN. AFTER PERT. 

 I I I 

 200 220 240 



300 



Fig. 1. Retardation and regres.sion of Echinarachnius egg: cleavage in urethan. 

 Progress of clea\age with time, observed in living Echinarachnius eggs. Control 

 cleavage reached 50% at 110 minutes and neared completion at 130 minutes. Exposure 

 to 22 mM urethan resulted in temporary furrowing at 140 and 180 minutes. Then 

 first and second cleavage proceeded simultaneously as a result of mult ii tie cleavage. 



so that two figures formed and divided the egg simultaneously into four 

 cells. As the dose is increased, this abortive phase is also suppressed and 

 cleavage comes much later. There is also some abortion of the second at- 

 tempt at cleavage, represented by the hump at 180 minutes. 



Table 1. Variants of esters and n-substituted carbamates* 



HXHCOOCH3— methyl carbamate 

 HXHCOOCH.CHoCHa— propyl carbamate 

 HNHCOOCH2CH3— ethyl carbamate 

 CeHsNHCOOCH.CHs— ethyl-X-phenyl carbamate 

 (CH2CH3)2NCOOCHoCH3— ethyl-N,N-diethyl carbamate 



* Examples from a larger series: J. Nat. Cancer Inst. 10: 1123, 1950. 



This pattern, then, describes the dividing egg's response to carbamates 

 and shows at least the visible mechanism involved. The pattern is typical 

 of a number of carbamates. Table 1 shows a few possible configurations 

 produced by substituting at one end or the other of the molecule. If, then, 

 we get the same pattern of cytological response regardless of the altera- 

 tions we make in the ends of the molecule, it appears logical, at least as a 

 naive first assumption, to say that the ends do not control the reaction that 



