98 Microscopic Histochemistry 



When using Nile blue, it should be remembered that it is 

 not a specific lipid stain. While the Sudans stain lipids and 

 nothing else, not all structures stained either red or blue by 

 Nile blue are of a lipid nature. 



B) Fluorescence microscopy .—Msiny lipid substances flu- 

 oresce in ultraviolet light (oxidation products of cholesterol 

 and of various unsaturated fatty acids, vitamin A, ceroid, 

 etc. ) , but only the fleeting green fluorescence of vitamin A 

 is characteristic enough to be useful in histochemistry. For 

 the technical details of the demonstration of vitamin A the 

 reader is referred to the articles of Popper.^"^ 



A few attempts at the localization of vitamin A by chemical 

 reactions, such as the Carr-Price test, appear to have been 

 gross violations of the fundamental principles of histochem- 

 istry.^* Tissues were dehydrated in alcohol and treated 

 with a solution of antimony trichloride in chloroform. Of 

 course, such a treatment would remove all lipids, vitamin A 

 included, almost quantitatively. It is difiicult to see how the 

 positive reactions reported were obtained. 



C) Polarization microscopy.— This used to be considered 

 a valuable means for the distinction of doubly refractile 

 cholesterol from other lipids. However, Lison^^ has shown 

 that its results cannot be interpreted in a chemically mean- 

 ingful way. In the case of lipids, birefringence appears to 

 depend largely on factors other than chemical constitution 

 ( such as state of aggregation, supercooling, the nature of the 

 mounting medium, etc. ) even in the case of pure compounds; 

 the behavior of mixtures is unpredictable. The sensitivity of 

 the method is poor; lipid mixtures containing less than 5 per 



27. Popper, H.: Proc. Soc. Exper. Biol. & Med., 43:133, 1940; Popper, H.: 

 Arch. Path., 31:766, 1941; Greenberg, R., and Popper, H.: J. Cell. & Comp. 

 Physiol., 18:269, 1941. 



28. Bourne, G.: Australian J. Exper. Biol., 13:239, 1935; Joyet-Lavergne, 

 P.: Protoplasma, 28:131, 1937; Joyet-Lavergne, P.: Compt. rend. Soc. de 

 biol., 126:650, 1937; Jones, O. P.: J. Lab. & Clin. Med., 32:700, 1947. 



29. Lison, L.: Bull, d'histol. appHq. a la physioL, 10:237, 1933. 



