SECTION ONE 



another hypothesis advanced earher (MacConaill, 1949, 1951), that 

 the erythrophile substance of the neuraxon is basic in reaction 

 and that dyes which stain it also stain red blood corpuscles and 

 the nucleolus of the nerve cell. We also discovered a new series 

 of dyes, as mentioned above. 



Although acid fuchsin is generally regarded as an acid dye, it 

 is really amphoteric as its formula (page 68) indicates. As a 

 dye, acid fuchsin stands out alone*. For many years it has 

 been one of the most widely used plasma stains. It has also been 

 used for a large number of special purposes in biology. But one 

 very important point about this dye seems to have passed un- 

 noticed until recently, and that is that it is the only dye which 

 contains three unsubstituted amino (basic) groups and the same 

 number of acidic (sulphonic) groups. In this respect alone, acid 

 fuchsin is unique. No other acid triphenylmethane possesses even 

 one unsubstituted amino group. Acid fuchsin has three. Some 

 acid dyes of other groups possess unsubstituted amino groups, 

 but the latter are in all cases outnumbered by acidic groups (e.g. 

 sulphonic and/or carboxyl) also forming part of the dye- 

 molecule. 



Theoretically, acid fuchsin could attach itself to either basic 

 tissue elements, by one or more of its sulphonic groups, or to acidic 

 tissue elements by one or more of its amino groups. In fact it 

 appears to combine with basic tissue elements only, whence its 

 function as an acid dye. The three amino groups of this dye are, 

 therefore, available for conjunction with acid groups of other 

 chemical substances, both in vitro and in a stained specimen of 

 tissue {in tela). This gives the possibility of combining acid 

 fuchsin with other acid dyes to form compound fuchsinic acids. '\ 

 It should be possible to form three such compounds corresponding 

 to a conjunction of the acid fuchsin molecule, through its amino 

 groups, with one, two, or three molecules of certain other acid 

 dyes, through their sulphonic groups. If the molecule of acid 

 fuchsin is represented as Fa, and the other acid dye as D, then 

 the possible compounds can be represented by FaD, FaD2, and 

 FaDs. Complete sets of such compounds have been prepared 

 and isolated in the pure state ; and they explain the colours found 



* But see chlorazol black structure (page 45). This dye, like acid fuchsin, 

 1 really amphoteric and worthy of further investigations. 



t Note: Fuchsinic acid is a synonym for acid fuchsin. 



77 



IS real 



