94 Microscopic Histochemistry 



wise tingible substances by even a thin layer of water-repel- 

 lent lipid may block the contact between the interior of the 

 particle and the dye solution. 



Owing to the similarity in the physical properties of the 

 lipids as a group, sharp separation of the individual sub- 

 groups is a formidable task even in conventional preparative 

 chemistry, and an impossibility in histochemistry. Some de- 

 gree of selective removal or preservation of certain compo- 

 nents can be accomphshed, but the results are not even re- 

 motely quantitative. Another complicating factor is the pro- 

 tective action of proteins. For instance, kerasin is extractable 

 from ground-up tissue by hot methyl alcohol or chloroform, 

 but it is almost insoluble (especially after formahn fixation) 

 while combined with protein within intact cells. ^ 



This complexity of the situation makes the histochemical 

 analysis of lipids very difficult and often illusory. Even the 

 results of model experiments, which have been done in fairly 

 large numbers^' ^' '^' ^ since Altmann's original attempt in 

 1890, cannot be accepted at face value. The "pure" sub- 

 stances used were mostly biological concentrates the purity 

 of which is highly questionable. If model experiments are to 

 possess the force of proof, they must be performed with syn- 

 thetic compounds the components of which (especially the 

 fatty acid moiety) are exactly known. So far, such experi- 

 ments have not been done on a comprehensive scale. 



4. Morrison, R. W., and Hack, M. H.: Am. J. Path., 25:597, 1949; Pearse, 

 A. G. Everson: J. Clin. Path., 2:81, 1949. 



5. Altmann, R.: Die Elementarorganismen und ihre Beziehungen zu den 

 Zellen (Leipzig: Veit & Co., 1890); Mulon, P.: BibHog. anat., 3:208, 1904; 

 Camus, J., and Pagniez, P.: Compt. rend. Soc. de bioL, 59:701, 1905. 



6. Smith, J. L., and Muir, W.: J. Path. & Bact, 13:14, 1909. 



7. Escher, H. H.: Corresp.-Blatt f. schweiz. Aerzte, 49:1609, 1919; Kauf- 

 mann, C, and Lehmann, E.: Zentralbl. f. allg. Path. u. path. Anat., 37:145, 

 1926; Kaufmann, C, and Lehmann, E.: Virchows Arch. f. path. Anat., 

 261:623, 1926; Kaufmann, C, and Lehmann, E.: ibid., 270:360, 1928; 

 Baker, J. R.: Quart. J. Micr. Sc, 88:463, 1947. 



8. Cain, A. J.: Quart. J. Micr. Sc, 89:429, 1948. 



