346 E. T. Bell, 



Kasarinoff [1910] uses Ciaccio's method to distinguish true fats 

 from Hpoids. 



Smith, Mair, and Thorpe [1908] studied the principles under- 

 lying Weigert's method of staining medullated nerves. They have 

 shown that as a result of the hichromate treatment chromium combines 

 with unsaturated fat to form a substance that is insoluble in alcohol, 

 xylol, etc., and therefore not removed in the process of embedding 

 in celloidin or paraffin. The chromated fat lakes haematoxylin giving 

 the characteristic purple stain. By using a saturated solution of po- 

 tassium bichromate at 39° C or 65° C, they have shown that the bi- 

 chromate-haematoxylin method will stain oleic acid, elaidic acid, 

 erucic acid, undecylenic acid, triolein, and also certain loose com- 

 binations of Cholesterin and fatty acid that give myelin figures. Amyl 

 alcohol and cetyl alcohol are also stained. They even succeeded in 

 staining ordinary connective tissue fat cells by strong bichromate 

 treatment. In a later paper [1910] Smith and Mair state that the 

 substance in the medullary sheath that stains by Weigert's method 

 is a cerebroside. They also add that Cholesterin may be stained if the 

 temperature is kept at 145° C during the bichromate treatment. They 

 believe that the staining ,, depends upon the presence in the molecule 

 of an unsaturated group or of an alcohol or aldehyde radical". Sub- 

 stances in the fluid crystalline condition stain much more rapidly 

 by the bichromate-haematoxylin method than other fatty bodies. 



Sudan III, as employed by Giaccio, is better than haematoxylin 

 to stain the chromated fat since the former stain is much more selective. 

 However Smith's work indicates that the Giaccio method does not 

 distinguish true fats from lipoids. 



By making smears of oleic acid and triolein, obtained from Kahl- 

 baum, on cigarette paper (Wlassak's method) and treating them by 

 Giaccio's method, I have found that both these substances give positive 

 results. It is very noticeable that a great many droplets appear as 

 hollow rings with a clear center. Apparently only the periphery of 

 the droplet is chromated. The central portion not being oxidized is 

 dissolved. This would seem to explain the ring-droplets obtained by 



