STAINING, PRACTICAL AND THEORETICAL 



FUCHSINIC ACID DYES 



It has recently been discovered (M. A. MacConaill & E. Gurr, 

 1959-62; E. Gurr & M. A. MacConaill, 1959-62) that certain 

 acid dyes will unite chemically with certain other acid dyes to 

 form compound stains which impart polychromatic pictures to 

 tissue preparations viewed under the microscope. The first three 

 compound dyes of the series were originally given the name of 

 the MG or Falg dyes, for want of a better name at the time. 

 Later the name was changed to the Falgic acids, for reasons 

 explained below (page 78). 



The discovery came about during the course of an investigation 

 which was originally intended to serve a dual purpose, namely : 



1. As a continuation of an earlier study (MacConaill, 1949,* 

 195 1) upon the erythrophile elements found in the nervous sys- 

 tem, including the so-called neurokeratin. The elements men- 

 tioned were called erythrophile because they had a special affinity 

 for the red dye, acid fuchsin. The latter dye belongs to the 

 triphenylmethane group, which is a division of the triarylmethane 

 group of dyes. It seemed desirable to carry out a comparative 

 study of the effect of other dyes of the same group, and of other 

 groups, as a preliminary to more detailed work upon the ery- 

 throphile substances themselves. 



2. As a test of another hypothesis (E. Gurr, i960) regarding 

 the influence of molecular weights of acid dyes on their staining 

 effects. According to this hypothesis, acid dyes of high molecular 

 weight do not usually stain close-knit tissues, while dyes of low 

 and medium molecular weights usually stain close-knit tissues 

 preferentially. Dyes of the former class usually stain close-knit 

 tissues lightly, if at all. 



During the early stages of our work (1959, i960) on neuro- 

 logical tissues, our experiments took the form of using a series of 

 acid triphenylmethane dyes having molecular weights ranging 

 from 536 to 808, as well as a series of acid dyes from other groups, 

 having molecular weights from 580 to 759. We were able to 

 confirm the hypothesis regarding molecular weights of acid dyes 

 on the material investigated. We were also able to confirm 



* See page 258. MacConaill's Lead Haematoxylin-Acid Fuchsin Tech- 

 nique. 



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