210 INJURY, RECOVERY, AND DEATH 



in which the tissue lies is open to the objection that sub- 

 stances are absorbed on the surfaces of the cells and in 

 the spaces between them, and it is impossible to say what 

 actually penetrates the protoplasm. 



Others have attempted to analyze the cell sap. The 

 most favorable cells for this purpose are those of plants, 

 since they contain, as a rule, vacuoles filled with sap. In 

 general, the method has been to crush the tissues and 

 express the sap, but it is obvious that this procedure 

 involves too many possibilities of error. 15 



The entrance of dyes has been extensively investi- 

 gated, but this method is beset by many pitfalls, 16 and the 

 results hitherto obtained are confusing. 



"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 and cell walls. 

 The degree of pressure used in expressing has a marked influence on the 

 concentration of the sap. Cf. Mameli (1908), Dixon and Atkins (1913) 

 Gortner and Harris (1914), Gortner, Lawrence and Harris (1916). 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. 



" To a great extent the coloration of the cell by a dye shows the 

 extent to which the dye can combine with substances within the cell 

 rather than the rate at which the dye penetrates. Thus many cells contain 

 substances which combine with methylene blue so that it becomes far 

 more concentrated within the cell than in the external solution (Pfeffer 

 1900, 1:96). Unless the cell has this power it often fails to appear colored 

 even though it may contain the dye in the same concentration in which 

 It exists outside. In such cases it may sometimes be detected by plas- 

 molyzing the cell and thus concentrating the dye. A further complication 

 is that a cell may appear to have taken the dye into its interior when in 

 reality only the surface or the cell wall is stained. There are many 

 other difficulties, which need not be discussed here, such as toxic action 

 of the dye and changes in the dye ( decolorization etc.) as it enters the 

 cell. A very serious objection to this method is that it does not give 

 quantitative results. A review of the literature will be found in 

 Hober (1914). 



