METACHROMASY 245 



but whereas the basic ones are important in microtechnique and 

 all act on the same chromotropes, apparently in essentially the 

 same way, the acid metachromatic dyes are relatively unimportant 

 and act quite differently from the basic ones. 



The metachromasy of basic dyes will be dealt with first. 

 Unnecessary repetition of the words 'of basic dyes' will be avoided. 

 All general remarks on metachromasy are to be understood as 

 referring to the metachromasy of basic dyes, unless the contrary is 

 clearly indicated. 



Metachromasy is of importance in histochemistry, because very 

 simple techniques give striking results that help towards the 

 chemical identification of tissue-constituents. 



The most obviously chromotropic tissue-constituents are the 

 following: — 



the matrix of cartilage ; 



the secretions of certain mucous glands ; 



the granules of the basiphil cells (Mastzellen) of connective 



tissue ; 

 the corpuscles of amyloid degeneration ; 

 the 'volutin' granules that occur in yeast and in certain 



diatoms and bacteria. 



Certain substances prepared from the cell-walls of various red 

 algae are strongly chromotropic. Agar is an example. 



Various tissue-constituents other than these are also chromo- 

 tropic, but less strikingly so. Chromatin is an example of a weakly 

 chromotropic substance. All chromotropes that occur in micro- 

 scopical preparations are basiphil, though not all basiphil objects 

 are chromotropic. 



The first person to study metachromasy in detail by the examina- 

 tion of pure substances in glass vessels was Lison,^^^ whose work 

 has been extended by Sylven.*^^ 



A large number of substances that are very familiar components 

 of organisms are not chromotropes. The following are examples: — 

 t/-ribose, sucrose, maltose, cellobiose, lactose, dextrins, glycogen, 

 starch, hemi-cellulose, cellulose, inulin, gums, mucilages, pectic 

 substances; serum-albumin, serum globulin, fibrin, collagen, 

 keratin, myosin, silk. No lipid is obviously chromotropic, though 

 cerebrosides may perhaps be feebly so. It is characteristic of 

 chromotropes that they are acidic, and this is of course related to 



