84 CYTOCHEMISTRY OF ALDEHYDES 



by a factor of, say, fourfold. If there is no significant difference 

 in the intensity of the reaction which is found, there cannot be a 

 significant loss of activity in any of the steps. Thus with liver 

 tissue it has been found that the procedure given on page 80 does 

 not cause any destruction of liver aldehyde. 



The Detection of Diffusion Artefacts 



The amount of attention which has been paid to the elimina- 

 tion of diffusion artefacts in the cytochemistry of aldehydes is 

 very small. Indeed, it may be said that most investigators have 

 displayed a remarkable resistance even to considering the possi- 

 bility that their results may be complicated by diffusion arte- 

 facts. Stedman and Stedman (1943) performed a very valuable 

 service when they drew attention to the fact that the procedure 

 of hydrolysis in N hydrochloric acid depolymerizes thymonucleic 

 acid and suggested that this depolymerization may perhaps in 

 some cases be sufficiently serious to make the nucleic acid dif- 

 fusible. Following the observations of the Stedmans, I was able 

 to show that, when purified thymonucleic acid is treated by the 

 Feulgen method, a readily soluble fraction is formed. The pro- 

 cedure was simply to suspend thymonucleic acid in N hydro- 

 chloric acid at 60° C. After hydrolysis for 10 minutes the sus- 

 pension was filtered, the filtrate neutralized, and reduced fuchsin 

 solution added. A deep purple colour immediately developed. 

 This coloured solution readily stains tissue sections and such prep- 

 arations as squashes of Drosophila salivary glands. The distri- 

 bution of stain in these specimens is very similar to that found 

 in the Feulgen reaction, except that the nucleolus is more deeply 

 stained than is normally found, and there also may be some 

 staining of the cytoplasm. It is, therefore, difficult to be certain, 

 without the use of diffusion studies, whether the results obtained 

 by the fuchsin technique for thymonucleic acid are complicated 

 by diffusion artefacts. This is particularly true so far as the 

 fine detail of distribution of thymonucleic acid is concerned. It 

 would not be difficult in any given instance to discover whether 

 a significant amount of diffusion does in fact occur, if the super- 

 imposed section technique, referred to in earlier chapters of this 

 book, were used. But I am not aware of any instance in which 

 this procedure has in fact been used. It is likely that any diffu- 

 sion artefact which does occur would be eliminated, or at least 



