Inorganic Substances 39 



tinguishable from that of Prussian blue (ferric f errocyanide ) . 

 This technique is not recommended because it invariably 

 produces minor, and sometimes major, artifacts. ^^ Ferrous 

 sulfide is attacked by the acid in an explosive way, resulting 

 in the deformation of the solid granules into balloon- and 

 burr like structures with a light center and dark outlines. 



It should be mentioned here that no reaction is ever ob- 

 tained in animal tissues under either normal or pathological 

 conditions if acidified ferricyanide is applied directly to the 

 sections. ^*^ This shows absence of ferrous iron. 



A few other methods will be mentioned briefly. Macallum^ ' 

 suggests the use of hematoxylin, which forms a blue-black 

 lake with iron. It is easy to show that under strictly neutral 

 conditions hematoxylin will not stain any iron in the tissues. 

 Positive reactions are obtained only after treatment with acid 

 (exposure to sulfuric acid-alcohol,-^ fixation in Bouin's fluid 

 or even in unneutralized formalin ) . Such treatment is wrong 

 in principle, as has been pointed out. In addition to pro- 

 ducing diffusion artifacts, the specificity of the method is 

 poor. Other m^etals such as lead and copper (under experi- 

 mental and pathological conditions) will give reactions indis- 

 tinguishable from that of iron. Moreover, dichromate fixation 

 may cause unsaturated fatty substances (myelin, etc.) to 

 stain very intensely.-^ 



The thiocyanate technique^^ is unsuitable for localization 

 because the red coloration obtained with it is highly diffusi- 

 ble. Schmelzer^^ recommends the application of HCNS gas 

 to sections mounted in paraffin oil, and he claims good locali- 

 zation. 



26. Gomori, G.: Am. J. Path., 12:655, 1936. 



27. Macallum, A. B.: J. Physiol., 22:92, 1897. 



28. Dieterle, R. R.: Arch. Path., 10:740, 1930. 



29. Miihlmann, M.: Virchows Arch. f. path Anat., 266:697, 1927. 



30. Kockel, H.: Virchows Arch. f. path. Anat., 277:856, 1929. 



31. Schmelzer, W.: Ztschr. f. wissensch. Mikr., 50:99, 1933. 



