434 COLLOIDS IN BIOLOGY AND MEDICINE 



Another favorite nuclear staining method is with the mordant dyes, 

 e.g., hematoxylin or carmine. In this instance, also, the acid char- 

 acter of the nuclear proteins explains the action of the dyes. The 

 nuclear proteins adsorb the mordants, usually colloidal aluminium 

 hydroxid (from alum), and these form an insoluble compound with 

 the acid hematoxylin or one of its oxidation compounds, or with 

 acid carmine. 



Finally, we may mention the double staining of ROMANOWSKY, 

 which has been modified by G. GIEMSA. Its underlying principle 

 is that a basic blue dye (methylene azur or methylene blue) is mixed 

 with an acid dye eosin (see p. 426). At first the preparation stains 

 blue in the mixture; gradually there occurs a differentiation into 

 blue and red elements or combination violet shades whereby the 

 nuclei become red. For the present, all interpretations of this phe- 

 nomenon are quite hypothetical ; it presents a very interesting colloid- 

 chemical problem. If methylene azur and eosin are mixed, a colloidal 

 solution of eosin-acid-methylene azur forms, provided that one of the 

 two dyes is present in excess. Nuclear staining may occur in such 

 a way that the basic methylene azur serves as mordant for the eosin; 

 it is also possible that the nuclei stain better with colloidal eosin- 

 acid-methylene azur than with crystalloidal methylene azur, and that in 

 a reaction which requires time (possibly hydrolytic cleavage) the red 

 color base of methylene azur becomes free. In this double staining 

 there enter as factors phenomena involving the colloidal condition 

 of both dye and specimen with respect to the diffusibility of the dye 

 and perhaps also other circumstances which have not been consid- 

 ered here. This may be assumed both from the accurate directions 

 which are given for the preparation and age of the solution, the 

 thickness of the preparation, the duration of staining, etc., and 

 from the fact that every departure from the directions gives a dif- 

 ferent result. 



Connective Tissue, Capillary Walls, Membranes, Etc. 



From the numerous reports I gather that only easily diffusible 

 stains, especially the sulphoacids (acid fuchsin, soluble blue com- 

 bined with picric acid), are suitable for this purpose. This probably 

 depends upon the fact that connective tissue, etc., are among the 

 tissues poorest in water and least swollen, so that dyes of more col- 

 loidal character are unable to penetrate them. 



For the staining of elastic fibers, which is best performed by the 

 orcein method of P. G. UNNA and TAENZER or by WEIGERT'S method, 

 we have no explanation whatever. The recent investigations of the 

 keratins by L. GOLODETZ and P. G. UNNA show that we are dealing 



