114 



INFLUENCE OF TEMPERATURE ON BIOLOGICAL SYSTEMS 



axis becomes proportionally slower as this weakening of the gel system 

 progresses; and 3) that furrowing is aborted completely at 6,000 lb/in-, 

 (at 23°C), when the weakening of the plasmagel system has reached a 

 certain critical level. 



Ahhoiigh the pressure block to cleavage was first observed in the egg 

 of Arbacia 'punctulata, many other eggs, derived from animals in five 

 different phyla, have now been studied (27). The minimum pressure re- 

 quired to block the furrowing reaction shows some variation, to be sure, 



o 



z 



IxJ 



UJ 

 O 



UJ 



> 



UJ 



3 



140 



120 



100 



80 



60 



y 40 



UJ 



20 



ISO 



too 



40' 



I0» 



TEMPERATURE 

 15* 20» 25* 



UNFERT. EGGS ARBACIA PUNCT. 



I0« 



25« 



30« 



I5» 20" 



TE M PE RATURE 



Fig. 2. Plasmagel strength in relation to temperatvne. Data from Marsland, 1950. 



but in each case there is a critical blocking pressure and usually this 

 falls in the range of 4,000-6,000 lb/in.- (at 20°-25°C). 



At pressures below 6,000 lb/in.-, the furrow (of Arbacia) does not 

 recede, but the rate at which it cuts through the egg is definitely retarded. 

 At the 4,000-lb. level, for example, it takes 9 minutes for the furrow to 

 pass from the equator to the spindle center, instead of the normal atmos- 

 pheric time of 3 minutes (at 23°C). Thus the curve obtained by plotting 

 the log of this retardation as a function of pressure gives an excellent 

 fit when superimposed upon a similar plot of the cortical gel strength in 

 relation to pressure, measured at the time when the furrows are about 

 to form (fig. 1). 



