CYTOPLASM 



147 



finally rise again, since in that case the cytoplasm would solidify as a 

 result of shrinkage. Death with coagulation occurs at about 42° C. 



Since in the physiological temperature range a rise in temperature 

 would certainly not be able to rupture either heteropolar cohesive 

 bonds or main valency bonds, it is permissible to attribute the change 



Fig. 97. Viscosity of the cytoplasm of the amoeba (from Heil- 



BRUNN, 1930). Abscissa: temperature in °C. Ordinate: viscosity 



(time in seconds, which a crystal enclosed needs to travel halfway 



through the cell under the influence of gravity). 



in viscosity of the cytoplasm primarily to the abolition of homopolar 

 cohesive bonds. The weakness of the homopolar cohesive bond is 

 demonstrated by the exceedingly small surface tension of proto- 

 plasmic membranes (i dyne/cm against nutrient. Table XXI, p. 166), in 

 comparison with water (71.6 dynes/cm against air. Table V, p. 43), 

 where the surface is formed by heteropolar HgO molecules. 



11. Heteropolar cohesive hands are of a quite different character. The 

 underlying attractive forces are due to dipole moments (p. 19), 

 which are mostly so strong that they are designated as secondary or 

 residual valencies. 



Of recent years the semi-chemical character of heteropolar cohesive 

 bonds has come to the fore, since they are designated as hydrogen 

 bonds or hydrogen bridges (Pauling, 1940). Wherever dipolar groups 

 with hydrogen atoms situated in the periphery (OH-, NHg-groups) 



