SECTION ONE 



carboxyl groups for their acidity just as does eosin itself. Eosin 

 will, however, unite with basic dyes (methylene blue, for instance) 

 in the absence of competition as mentioned on page 32. 



A striking example of staining due to both physical and chemical 

 factors is to be found in the strongly acid dye, solochrome cyanin 

 R. The molecule of this dye, as can be seen from the structure 

 on page 72, contains two carboxyl groups and one sulphonic. 

 There are no basic groups, on the dye-ion, which might impart 

 amphoteric properties. The dye-ion is wholly acid. Therefore it 

 is rather surprising that this dye acts towards tissues as though 

 it were an amphoteric dye. Gurr & MacConaill (1959) found 

 that this dye, like the closely related dye used by Pearse (1957), 

 acts as if it were acid towards basic tissue-elements, and as if it 

 were basic towards acid tissue elements, notably DNA and RNA. 

 As a test of an earlier hypothesis (MacConaill, 1949, 1951) 

 regarding the relative basicity of the erythrophile elements that 

 we included solochrome cyanin in the group of dyes used in our 

 investigations. Given a suitable pH, solochrome cyanin R stains 

 acidic tissue elements blue, and basic elements pink or red. 

 Pearse first used a 2% solution of orthophosphoric acid to secure 

 a suitable pH. In our work we found that Pearse's results appear 

 to be reproduced equally well by using acetic acid as the dye- 

 solvent. We also found that the best results were obtained with 

 a 0'5% solution of the dye. The only difference between the 

 dye used by Pearse (1957) and that used by us was that his was 

 a monosodium salt and ours a trisodium salt. 



Staining by solochrome cyanin R fully confirmed the inference 

 that led us to the trial. The special elements (MacConaill, 1949, 

 1951) of the spinal cord, including the neurone nucleolus, showed 

 a basic reaction, while those tissue elements that had been deemed 

 to be acidic reacted correspondingly to this dye. 



The molecular structure of solochrome cyanin R is such that 

 there is no reason to think that it breaks up into an acidophil and 

 a basophil portion when in solution. Solochrome cyanin is a 

 hydroxytriphenyl methane dye, the colour changes of which are 

 probably due to dissociation of its hydroxyl group as occurs in 

 the case of the phthalein class of indicators. The latter may 

 also be regarded as hydroxytriphenyl methane derivatives, 

 Solochrome cyanin, therefore, may be looked upon as an indi- 

 cator, rather than as a dye. For this reason we consider it 



