235 



sudden lowering' of the teniix'i'Mtui'e, and an imniersion 

 in M/lOO sucrose the same effects as a slow cooling. 



In cooling- experiments of the same type with Monas, 

 Greeley (1902) described a typical sporulati(m caused 

 by low temperature. At +4 resting- cells were formed 

 which, when exposed for 5 to 7 days to +1% divided into 

 several spherical spores (from 2 to 25 in a cell). So the 

 physiologT,cal processes involved in reproduction by 

 spores seem to bear some similarity with those which 

 lead to injury and death. 



(})) Gehenio and Luyet (1939) found that the Plasmo- 

 dium of the myxomycete Physarmn polycephalum w^as 

 killed by sudden or moderately rapid exposure to cold at 

 temperatures above the freezing point. They described 

 the following phenomena as stages in the process of 

 death, when the temperature of the organisms was low- 

 ered gradually from room temperature at the rate of one 

 degree per minute: 1. At +5° to 0°, movement ceased; 2. 

 At +3° and below, hyaline vesicles formed; 3. At 0' or 

 below, the protoplasm underwent disorganization; 4. At 

 the same temperature the pigment granules broke down. 

 A sudden cooling to a given low temperature w^as consid- 

 erably more injurious than a slow cooling to the same 

 temperature. 



■ The authors propose the following interpretation of 

 their observations. Under the action of the lowering of 

 temperature the protoplasmic sol would set gradually to 

 a gel. They relate this hypothetical gelation to the in- 

 crease in viscosity wdiich was noted by Heilbrunn (192-1:) 

 in protoplasm cooled to a temperature slightly above zero 

 and to the cessation of protoplasmic streaming. But the 

 gelation ' 'would be a reversible process preceding death 

 and not constituting death. . . .After complete setting, 

 the gel would undergo a syncretic breakdown, squeezing 

 out the dispersion medium enmeshed within it, and this 

 would be the death process itself. At the periphery of 

 the i)lasmodiuni the locally expressed fluid would appear 



