Organic Substances 95 



HiSTOCHEMICAL METHODS FOR LiPIDS 



Fixation.— In some cases (especially when true chemical 

 reactions are employed) it may be preferable to use fresh, 

 unfixed tissues, because fixation may modify the reactive 

 groups. In other cases such modifying effects are used de- 

 liberately ( see p. 101 ) . 



As a routine fixative, formalin is the best and simplest, es- 

 pecially when about 1 per cent CaCL is added to render 

 phospholipids insoluble ( Baker ).^ Millot and Giberton^^ re- 

 port that prolonged fixation in formalin will lead to a pro- 

 gressive decrease in the amount of total fat and also to an 

 increase in the proportion of free fatty acid. The description 

 of their experiments is not clear enough to permit a judgment 

 as to the validity of their conclusions. 



Of course, embedding either in celloidin or in paraffin will 

 remove lipids more or less quantitatively unless they are 

 made insoluble first (by special treatments, such as pro- 

 longed chromation). Embedding in carbowax (Blank,^^ 

 Firminger^^ ) , on the other hand, appears to be a usable pro- 

 cedure. For most purposes it is simplest to use frozen sec- 

 tions. They should not be exposed to concentrations of alco- 

 hol higher than 70 per cent, and even this may cause the 

 solution of the finest droplets. 



The actual procedures of demonstration will be divided 

 into two groups— physical and chemical. 



Physical Methods 



A) Staining with oil-soluble dyes.— There is a large num- 

 ber of oil-soluble dyes known, many of which are suitable for 



9. Baker, J. R.: Quart. J. Micr. Sc, 87:441, 1946. 



10. Millot, J., and Giberton, A.: Compt. rend. Soc. de biol., 97:1674, 

 1927. 



11. Blank, H.: J. Invest. Dermat., 12:95, 1949. 



12. Firminger, H. J.: Stain Technol, 25:121, 1950. 



