SELECTIVE PERMEABILITY 345 



dispersing phase and which underwent the same process (was 

 drawn together) as the other colloidal phases in the plasma- 

 solution. These water filled channels are, according to Lepesh- 

 kin, the cause of the loss of the property of selective permeability 

 by the cell on the solidification of the protoplasm as they allow 

 the passage of any substance which is soluble in water. He 

 emphasizes the analogy in this respect between the plasma- 

 membrane and the artificial membranes made for the purpose 

 of studying osmotic pressure. The artificial membranes are 

 also solutions which have a tendency to solidify and form water- 

 filled channels, for which reason they are to be kept in constant 

 contact with the membrane forming solution in order to preserve 

 their efficiency. ^- 



The coagulation of the plasma-membrane can be obtained, 

 according to Lepeshkin, by means of mechanical force, heating, 

 and use of chemicals. 



That the membrane can be coagulated by mechanical force 

 is shown, as he believes, by the behavior of a Spirogyra cell 

 under the influence of mechanical pressure which has been 

 referred to. That this is a case of coagulation and not of me- 

 chanical dismembering is shown, according to him, by the fact, 

 that the presence of alkalies in unfavorable for the described 

 behavior of the Spirogyra thread, while the presence of acids 

 is favorable — exactly as is the case with coagulation by heating. 



From the fact that the plasma-membrane is coagulated by 

 heating Lepeshkin draws the conclusion that it contains con- 

 siderable quantities of proteins, as it is the proteins which are 

 largely coagulated by heat. The behavior of the protoplasm 

 on heating would also tend to show that there is no difference 

 in protein content between the outer and inner layers as they 

 all coagulated simultaneously when the specific temperature is 

 reached. The heat of coagulation is higher than the normal in 

 the presence of alkali and lower in the presence of acids. This 

 is also in conformity with the behavior of proteins which are 

 completely coagulated only in an acid solution. ^^ 



^- Pfeffer, W., Osmotische Untersuchungen, pp. 25-26. 

 ^' Cohnheim, Chemic dor Eiweiszk(')rpcr, p. 131. 1904. 



