102 Microscopic Histochemistry 



used in microscopic technique as a "hardener," especially of 

 brain, for about one hundred years. Its effect on lipids con- 

 sists in their oxidation to a miscellany of compounds, some 

 of which are so insoluble as to be demonstrable by Sudan 

 dyes even in paraffin sections (Ciaccio).*^ Bichromate itself 

 is reduced at the sites, of oxidation to an insoluble compound 

 (Cr203?) which can combine with hematoxylin to form a 

 blue-black lake, quite resistant to differentiation. 



The rate at which unsaturated lipids chromate varies con- 

 siderably. It appears that the presence of hydrophilic groups 

 enhances chromation; e.g., phosphohpids chromate readily,** 

 and triolein chromates much faster if it contains a small 

 amount of cholesterol than in a pure state.*^ This is not sur- 

 prising, since potassium dichromate is lipid-insoluble. 



The optimal conditions for the chromation of phospho- 

 lipids have been studied carefully by Baker.^ As a result of 

 his studies, he succeeded in devising a sensitive and specific 

 modification of Lorrain Smith's method.^ The claims of 

 specificity have been confirmed by Cain.*^ 



Method 



1. Fix in formalin containing 1 per cent CaCl2. 



2. Transfer pieces directly to a 5 per cent solution of po- 

 tassium dichromate containing 1 per cent of CaCb and keep 

 them in it for 18 hours. 



3. Continue mordanting in the same solution for 24 hours 

 at 60° C. 



4. Cut frozen sections, preferably after gelatin-embedding. 



5. Mordant sections in the dichromate-calcium solution for 

 1 hour at 60° C. 



6. Wash sections in water and stain them in the following, 

 freshly prepared, solution for 5 hours at 37° C: 



43. Ciaccio, C: Zentralbl. f. allg. Path. u. path. Anat., 20:385, 1904. 



44. Ciaccio, C: Compt. rend. A. anat., 25:87, 1930. 



45. Dietrich, A.: Verh. d. deutsch. path. Gesellsch., 14:263, 1910. 



46. Cain, A. J.: Quart. J. Micr. Sc, 88:467, 1947. 



