432 COLLOIDS IN BIOLOGY AND MEDICINE 



may expect most valuable discoveries on the physiology and pathology 

 of living tissue as well as concerning the mechanism of the action of 

 drugs. E. GOLDMANN, R. HOBER and W. SCHULEMAN have in recent 

 years contributed much concerning the utilization and theory of vital 

 staining. They studied healthy and sick animals, whereas KUSTER 

 and RUHLAND applied vital staining to plants. As yet vital stain- 

 ing of bacteria and other microorganisms has not been definitely 

 attained (EISENBERG). The stain must not be poisonous or the cell 

 will die before it has the desired color. 1 We have numerous dyes at 

 present which fulfill this condition. A few of the most useful are 

 mentioned, methylene blue, neutral red, toluidin blue, trypan blue, 

 trypan red and isamin blue. The studies of RUHLAND on plants, as 

 well as those of EVANS, SCHULEMAN and WILBORN on animals, indicate 

 strongly that the extent of dispersion of the dye chiefly determines 

 its suitability for vital staining, so that the cell behaves like an utra- 

 filter (see p. 428). A dye that is too diffusible distributes itself too 

 readily in all the organs and is accordingly quickly excreted by them; 

 one that is highly colloidal remains at the site of injection. The 

 studies of RUHLAND include both basic and acid dyes while the 

 experiments of EVANS, SHULEMANN and WILBORN were only with 

 acid dyes. 



It was formerly believed that only lipoid soluble dyes penetrated 

 living tissues, but this view has not been sustained (see also GARMUS). 

 Many vital stains are known which are insoluble in fats. The col- 

 loidal metals are included among these; they have proven useful 

 agents in studying "distribution" in J. VOIGT'S method of investiga- 

 tion. This does not by any means imply that lipoid insoluble vital 

 stains may not be especially suitable for some of the organs which are 

 rich in lipoids. Thus, for instance, axis cylinder and ganglion cells 

 of the nerve substance are most intensely stained by methylene blue. 

 It is remarkable that the cell nucleus which stains most intensely 

 with basic dyes when the object is dead, with vital staining is con- 

 stantly colorless; nuclear staining occurs only when the cell dies. 



If vital stains are to be fixed, i.e., made insoluble, ammonium 

 molybdate, sublimate, picric acid, etc., are employed. 



If this fixation is omitted, the dye diffuses away after death, i.e., 

 according to the changed condition of the tissue, physical and 

 chemical, and a different distribution results* 



1 The lack of toxicity of vital stains is only relative; in concentrated solution 

 they are all poisons and may be used only in extreme dilutions. Safranin and 

 methyl violet, especially, are quite poisonous, and on this account they cannot 

 be employed for injections into the higher animals. 



