The Plasmatic Membrane. 
189 
temperature is lowered to 60-6 n C, not very far removed from 
Spirogyra in alkaline medium. These effects of acid and alkali are 
thus in accordance with their effects on coagulation of proteids 
n vitro. 
Incidentally Lepeschkin noted the interesting fact that the 
chloroplast of Spirogyra can he seen to coagulate at about 48°C; 
more than 2°C below the temperature coagulating the cytoplasm. 
Coagulation of plasma-membrane by mechanical stress. In non¬ 
living colloids coagulation by pressure has not yet been observed, 
but it is apparently quite easily produced in the cytoplasm of 
Spirogyra. It is not difficult to imagine that in a sufficiently 
complex colloidal structure, sudden pressure, which brought into 
contact the otherwise dispersed colloid particles, would lead to 
interaction between them resulting in their aggregating to larger 
masses, which is the essence of coagulation. 
Sudden pressure on filaments of Spirogyra , sufficient to rupture 
the cells, generally leads to complete coagulation of the cytoplasm. 
More gentle pressure first of all coagulates only the outer layer, and 
if the cells be previously plasmolysed this effect is very easily 
observed by the change of appearance of the plasma-membrane, 
such as was described for heat-coagulation. 
If a Spirogyra filament is kinked at one spot by being lifted up 
on a glass thread, local coagulation is produced just there and 
when the filament is subsequently plasmolysed the protoplasm is 
seen to be sticking to the wall at that spot, while pushed back else¬ 
where by the plasmolysing solution. 
Lepeschkin considers that he has seen recovery take place 
from small local spots of coagulation of the outer layer of plasmo¬ 
lysed cells, a very important indication of vital organisation tending 
to maintain the fluid condition of the protoplasm. Complete 
coagulation leads to chemical change and is thereby irreversible, 
being one of the chief causes of “ death ” of the cell. 
Even the stress of rapid plasmolysis and deplasmolysis may be 
sufficient to coagulate the protoplast, and the more rapidly these 
processes are carried out, the more effective they are in coagulation. 
Acids and alkalis have the same effect upon the susceptibility to 
mechanical stress as upon susceptibility to temperature. Thus a 
certain treatment of plasmolysis and deplasmolysis which coagulated 
76% of the cells of Spirogyra, only coagulated 6% after three-and-a- 
half hours in *05% Na„C0 3 ; whereas in another case preliminary 
treatment with ’01% citric acid doubled the percentage of coagulated 
cells, 
