MICROCHEMICAL TESTS 295 



there may be little difference between the various methods given 

 when one examines the slides. 



Validity of Method. This is recognised widely as a valid method. 

 The vitamin becomes black with silver nitrate and is found in 

 the form of scattered granules. For its connection with the Golgi 

 apparatus and mitochondria see Bourne [Aust. Jour. Exper. 

 BioL. 1936). The investigator will need to be careful in using 

 this silver nitrate method. The reagents should be pure, and the 

 vessels cleaned. At the present time no substance other than 

 vitamin C is known which in the dark is capable of reducing the 

 silver nitrate acetic acid solution. 



678. Microincineration.* This consists of incinerating paratfin sections 

 or smears in an electric furnace so that the organic material is removed 

 and the inorganic ash remains. The method is elegant, but strictly limited 

 in application. It was introduced into histology by the distinguished 

 French liistologist, A. Policard. The reader can obtain an idea of the 

 remarkable precision of the microincineration method by consulting the 

 paper by Horning in the Report of the Imperial Cancer Fund Laboratory, 

 1935, where a suitable electric furnace is described, and where a number 

 of excellent microphotographs is given. 



Microincineration is applicable to research on insoluble mineral 

 salts especially. It does not generally enable one to distinguish between 

 various mineral elements, as nearly all form a white ash. Iron gives 

 a red ash when it becomes the oxide (FcgOg). A reasoned evaluation 

 of the method will be found in Homing's paper {op. cit.). 



See also Policard, Bull. Hist., i, 1924 ; ibid., iii, 1926 ; ibid., iv, 

 1927 ; Policard and Okkels, Anat. Rec, xliv, 1930. 



* See § 1269. 



