266 



(cf. Cattell's review, ID.'Ui). Yeast takes more than four 

 thousand atmosi)heres (Liiyol, 1<>:'7). TnchT the action 

 of pressures of this nia^iiituck', ice sliould melt several 

 degrees l)eh)W zero. Besides, I'oi- ohtaiiiiii,^- sueli ])res- 

 sures it would be necessary to prevent the exi)ansion of 

 ice by holding it in some material more resistant than 

 the wjdls of an animal or plant tissue. 



The ex])eriiiients of Melseiis ( ISTO) who roiiiKJ that, 

 in a culture of yeast ex])osed in a steel boml) calculated 

 to burst at 8000 atmospheres, there were living cells after 

 the temperature was lowered until the bomb burst, are 

 also significant in the discussion of this problem. 



How enormous hydrostatic pressures have no action 

 on protoplasm while pricking with a glass needle may, 

 in some instances, start coagulation, is entirely unknown. 

 The answer to this question might throw some light on the 

 tyi)e of mechanical injury caused by ice. 



D. lljin (li)34) presented a new theory of death l)y me- 

 chanical injury, applicable to typical i)lant cells which 

 consist of a protoplast adhering to cell walls and filled 

 with cell sap. He distinguishes two general cases: that 

 in which death occurs during freezing and that in which 

 it occurs during thawing, and he subdistinguishes two 

 cases of death during freezing, that in which ice is formed 

 only in the intercellular spaces and that in which there 

 is ice also in the vacuoles. When death is caused by 

 thawing, the too rapid invasion of the protoplasm by 

 water would damage the living structure which is not 

 capable of expanding rapidly enough and is torn by 

 being pulled about. When death occurs during freez- 

 ing but without congelation of the vacuolar content, the 

 w^ithdrawal of water from the vacuole would cause the 

 latter to shrink and the protoplasmic layer, still attached 

 on one side to the cell walls, would be stretched between 

 these cell walls and the vacuole whose contraction it has 

 to follow; this stretching woud be injurious. In the ca§e 

 of formation of ice, both around the cell and in the vac- 



