263 



eiit century this idea has generally been aljancloned by 

 the physiologists, though occasionally some authors won- 

 der it' the reaction against it has been exaggerated. The 

 extrusion of water from the cells during freezing and the 

 absence of ice in the cells after the congelation of a tissue 

 have generally been observed after sloiv freezing as it 

 usually occurs in nature. With rapid freezing or when 

 the water content of the cells is very high, intracellular 

 congelation takes place (Molisch, 1897; and, more re- 

 cently, Stuckey and Curtis, 1938). The mechanical injury 

 in intracellular freezing may be quite different from that 

 of the generally observed extracellular formation of ice. 



Stuckey and Curtis {loc. cif.), who reported to have ob- 

 served ice formation within the cytoplasm itself in the 

 cells of the prothallia of Polypodium aureitm, claim that 

 death always resulted from such intracellular freezing. 

 They consider death as due, according to all evidence, to 

 a mechanical injury by ice. 



B. While the authors cited above have established that 

 ice does not destroy the cells by bursting them or by tear- 

 ing their membranes, more recent investigators have sup- 

 posed that tiny ice crystals tear the protoplasm itself. 

 Maximov (1914) for example, attributes death partly to 

 the destruction of the fine structure of the protoplasm as 

 a result of mechanical injury. 



Stiles (1930) thinks that the formation of a new phase, 

 namely ice, constitutes a mechanical disturbance result- 

 ing in a breaking down of the colloidal system. The types 

 of protoplasm in which the separation of the materials on 

 freezing is followed after thawing by their restitution to 

 the former state, would not be killed, the other types 

 would. He assumes that, if the crystals be smaller, the 

 mechanical injury would be less, and several types of 

 protoplasm might resist freezing. As a means of induc- 

 ing the formation of smaller crystals he proposes the use 

 of lower freezing temperatures, according to the finding 

 of Tammann (1898) on the relation between the temper- 



