134 STAINING 



At one time, it was thought to be possible to distinguish between 

 " basophilous " and " acidophilous " tissue elements, according 

 to their affniity for basic or acidic dyes. Ehrlich {Du Bois 

 Jieymond's Archiv., 1879, p. 571) thought that the basic dyes 

 have a special affinity for the chromatin of nuclei and the acidic 

 dyes for the cytoplasm and intercellular substances. But we 

 have already seen that the same substance may take up either 

 kind of dye, according to the conditions present. Most staining 

 processes are undertaken on cells which have been acted on by 

 fixing reagents or by the so-called " mordants," and these may 

 reverse the natural behaviour to dyes. Ehrlich's statement 

 only applies in fact to cover-glass preparations fixed and dried 

 by heat, without the action of reagents. The acidic colours, 

 orange and acid fuschin. although they stain cytoplasm, may 

 give good chromatin differentiation when used as regressive 

 stains. Methylen blue is basic, but stains nerves. It has been 

 shown in fact, that by pre-treatment with solutions buffered 

 to various reactions, tissue normally acidophilic may be 

 stained with a basic dye, and one normally basophilic with an 

 acid dye. 



243. Intra-vitam Staining. It is clear that unless the cell- 

 membrane of a living cell is permeable to a dye, no constituent 

 of the cell can be stained by it. Most dyes appear to be more 

 or less toxic if they enter the cell. But, while alive, the latter 

 is to a large extent protected, since the dye may not obtain 

 entrance. A living Amceha is stained by very few dyes. Neutral 

 red, however, parses through the membrane and stains various 

 structures, while having no apparent effect on the activities of 

 the organism. The auricle of the frog's heart can also be stained 

 with this dye, while continuing its normal contractions. Used 

 in this way, the dye is applied in very dilute solution. Since 

 neutral red is a very sensitive indicator just about the neutral 

 point, the fact of its permeability and non-toxicity makes it a 

 valuable test for the presence of acid or alkali within the cell. But 

 neutral red in very dilute solution will inhibit nutosis as shown by 



V. MOLLENDORF. 



When a dye enters a living cell, it usually stains various granules 

 and structures contained therein, while at the same time it is 

 uniformly diffused through the liquid phase of the protoplasm. 

 If the process of staining is conditioned by phenomena at boundary 

 surfaces, simple undifferentiated protoplasm in the living state 

 should be incapable of staining, and this seems to be the general 

 experience. As regards the question of permeability to a given 

 dye, unless the cell is able to show that it is still alive by movement 

 or by contractility, it is clearly a matter of difficulty to be certain 

 that, when a particular dye enters, it does so during life or only 

 after it has destroyed the normal properties of the cell-membrane. 



