136 Microscopic Histochemistry 



or not all or most of these characteristics apply to all forms 

 of the pigment cannot be decided, because there are only a 

 few thorough studies available; in most reports only a few of 

 the properties are mentioned. In the writer's experience the 

 type and duration of fixation markedly affect staining prop- 

 erties. Dichromate or moderately prolonged fixation in for- 

 malin tends to enhance basophilia, the Schiff reaction, acid- 

 fastness, and affinity to fat stains after paraffin-embedding, 

 whereas alcohol or short fixation in formalin has the opposite 

 effect. The pigment granules in one section, even within one 

 cell, may exhibit considerable variation in staining intensity. 

 Minor species differences have been noted by Lee.^^ 



It appears that all the pigments in this group are of an 

 essentially similar nature. They all derive from the oxidation 

 and polymerization of unsaturated fatty acids and represent 

 various stages of one process. Staining reactions similar to 

 the ones mentioned will develop in droplets of unsaturated 

 fat injected into the tissues^^ and even in fats allowed to 

 stand in air.^^' ^^ Since the chemistry of the oxidation of un- 

 saturated fats is very incompletely understood, it is impos- 

 sible to specify just what varying degrees of such staining 

 properties as basophilia or acid-fastness could mean. How- 

 ever, since all transitions from one extreme to the other may 

 be observed in a single slide, it is doubtful whether any clas- 

 sification within the group is biologically meaningful. Ceroid, 

 for example, is probably only a late product in the matura- 

 tion of lipogenic pigments in general, although the process 

 may have been accelerated and have actually progressed 

 beyond the normal average. 



Gillman and Gillman's cytosiderin^^ appears to be a mix- 

 ture of hemosiderin with lipogenous pigment. 



25. Glavind, J., Granados, H., Hartmann, S., and Dam, H.: Experentia, 

 5:84, 1949. 



26. Lee, C. S.: J. Nat. Cancer Inst., 11:339, 1950. 



27. Hass, G. M.: Arch. Path., 27:15, 1939; Endicott, K. M.: Arch. Path., 

 37:49, 1944. 



28. Smith, J. L.: J. Path. & Bact., 11:415, 1906. 



