265 



experimentally with an apparatus consisting of a glass 

 tube on the end of which was a rubber bulb tilled with 

 a li(iuid and iinniersed vertically, the open end up, in a 

 tiask containing water. When the latter froze in the 

 flask, the level of the fluid in the tube stayed the same, 

 indicating 'that there was no pressure exerted on the rub- 

 ber bulb. Plateau, it seems, did not notice that the re- 

 sults of his experiment disagreed with the principle that 

 he invoked, he should have observed a lowering of the 

 level of the fluid in the manometric tube, if 'the cavity 

 around the bulb were expanding. 



lljin (1936), discussing the case of plant cells frozen 

 in water, conceives the mechanism of pressure by ice as 

 follows: The water in which the material is immersed 

 freezes first and forms a wall around the protoplast of 

 each cell. When, later, the sap of the vacuole freezes, the 

 protoplast is wedged between two masses of ice. On these 

 assumptions he calculates, for different forms of cells, 

 how much the volume of the protoplasm should give so as 

 not to be crushed by the ice formed in the vacuole. His 

 figures indicate that there is definitely a possibility of 

 some crushing action. If the cells are frozen in air, it is 

 assumed that the pressure might be exerted against the 

 frozen cell walls. The fact that the congelation of the 

 vacuolar sap is always followed by death is in agreement 

 with the concept of an injurious pressure effect of the 

 frozen sap. 



As a whole, both the problem of the existence of a 

 pressure in a frozen tissue and the problem of the effi- 

 cacy of pressure in causing death call for more experi- 

 mental evidence. 



A consideration of the enormous pressure required to 

 kill protoplasm makes one doubt the possibility of the 

 existence of such pressures in cells. Most of the tis- 

 sues of metazoa resist a hydrostatic pressure of sev- 

 eral hundred atmospheres. Protozoa and bacteria are 

 killed only at pressures of the order of 1,000 atmospheres 



