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F. F. Blackman. 
membrane. The first lot of experiments dealt with the coagulation 
of the “ Plasmamembran ” 1 which can be brought about by different 
agents and the light which such action throws upon the nature of 
the membrane. 
Heat-coagulation of the plasma-membrane. It is a characteristic 
of proteids alone among colloids to coagulate at sharply defined 
temperatures and the fact that protoplasm exhibits this property is 
strong evidence of the dominance of proteids in its organisation. 2 
If a plasmolysed cell of Spirogyra be slowly heated while under 
observation with the microscope the coagulation is made evident by 
the change from a smooth shining appearance of the plasma to a 
dull granularity. This takes place in a few seconds when the right 
temperature is reached, and there is also obvious increase of perme¬ 
ability, for the protoplast rapidly shrinks by escape of its contents. 
In Spirogyra the average temperature of coagulation is 50 , 5°C (+ 1° 
C). If the red epidermal cells of Tradescantia be plasmolysed with 
sugar and then heated up, strong shrinkage at 70-7 marks the 
moment of coagulation and increased permeability; as the anthyo- 
cyan does not escape till the coagulation is quite complete there 
results at first a visible deepening of the cell colour. It is interesting 
to find that if the same material be plasmolysed with glycerine, which 
penetrates the protoplast fairly easily, then there is a strong increase 
of volume at the moment of coagulation, instead of contraction. 
Further work provides a clue as to why the above two coagulation- 
temperatures are so far apart. This depends on the fact that the 
Spirogyra protoplast is acid and Tradescantia alkaline and it can be 
shown experimentally that a trace of acid ('1% citric) added to the 
plasmolysing sugar lowers the coagulation-temperature, while a trace 
of alkali ('1% Na 2 C0 3 ) raises it. With Spirogyra the acid may 
lower the temperature 5 n C from the normal and the alkali raise it 
5 n C. With Tradescantia in the acid medium the coagulation- 
1 Throughout his papers Lepeschkin uses the term “ Plasma- 
membran ” for the structure he is investigating. He regards 
this as including the superficial layer of the protoplast and an 
unknown depth of the underlying strata, possibly the whole 
thickness , for he will not commit himself to any definition of 
the Plasmamembran except that it is the layer which is the 
seat of the selective permeability. 
2 The conception of the relation of coagulation of proteins to 
temperature and the presence of acids and alkalis here given 
is that current a few years ago. Recent studies on the nature 
of the mechanism of heat-coagulation of proteins by Dr. 
Harriette Chick and Dr. Martin have raised onr knowledge 
to an altogether higher plane (see Journal of Physiology, Vol. 
XL1II, and British Association Report, 1911, pp. 281—286). 
