DIRECT AND INDIRECT DETERMINATIONS OF PER- 

 MEABILITY. 



By W. J. V. OSTERHOUT. 



{From the Laboratory of Plant Physiology, Harvard University, Cambridge) 



(Received for publication, November 21, 1921.) 



Lack of direct and satisfactory means of determining the penetra- 

 tion of substances into the living cell has greatly hampered the study 

 of permeability. Various indirect methods have been resorted to, 

 but their reliability must remain in question until a direct method 

 can be found for testing them. 



Investigators have sought to overcome this difficulty in various 

 ways. Some have made analyses of tissues, but it is evident that these 

 must include too much intercellular material to be satisfactory. 

 Analysis of the solution in which the tissue lies, in order to determine 

 what is absorbed, is open to the objection that substances collect on 

 the surfaces of cells, as well as in the cell walls and in the spaces 

 between them, so that it is impossible to say what actually penetrates 

 the protoplasm. Others have sought to analyze the cell sap. Plant 

 cells are most favorable for this purpose, since, as a rule, they con- 

 tain vacuoles filled with sap. In general the method has been to 

 crush the tissues and express the sap, but this procedure involves 

 many possibilities of error.^ 



^ Among these may be mentioned contamination of the cell sap by substances 

 present in the cell walls or intercellular spaces and chemical reaction between 

 the cell sap and the crushed protoplasm or the cell walls. The degree of pres- 

 sure used in expressing has a marked influence on the concentration of the sap 

 (c/., Mameli, E., Atli del r. inst. bat. de Pavia, 1908, xii, 285; Dixon, H. H. and 

 Atkins, W. R. G., Sci. proc. roy. Dublin Soc. N. S. 1913, xiii, 422; Gortner, 

 R. A., Lawrence, J. V., and Harris, J. A., Biochem. Bull., 1916, v, 139). 



The investigation of blood and other body fluids is open to the objection that 

 we do not know to what extent substances penetrate between the cells in reaching 

 these fluids. In many cases penetration into these fluids seems to present very 

 special features. 



275 



