CHAPTER XXIX 



MICROCHEMICAL TESTS FOR CERTAIN SUBSTANCES OTHER 

 THAN FATS AND CHROMATIN 



666. In this chapter are some methods for glycogen, iron, 

 copper, calcium and lead. It should be stressed that micro- 

 chemistry of tissues carried out by staining or otherwise treating 

 sections or smears is full of possible pitfalls. It needs a knowledge 

 of both organic and inorganic chemistry often of a highly 

 specialised nature ; only those methods which are fairly straight- 

 forward and which offer a good chance of success are given here. 

 Many of these methods used in modern histo-chemistry have been 

 worked out for mammalian tissues and when applied to inverte- 

 brate or plant tissues are of more doubtful value. Even such 

 apparently straightforward methods as those for glycogen are 

 not easy and unless special care is taken the results obtained will 

 not be of value. The reader is advised to consult Dr. Lison's 

 recent work " Histochimie animale : Methodes et Problemes," 

 Gauthier-Villars, Paris, 1936, which is devoted entirely to this 

 subject, and which discusses the value of each test in a critical 

 manner. The success of a number of newer biochemical colour 

 tests applied to sections and smears made in this laboratory has 

 not been impressive. 



Elsewhere will be found tests for chromatin, § 623 ; fats, § 650 ; 

 oxidation centres, § 888 ; and for materials in plant tissues, § 1337, 

 chitin, etc., § 1189. 



GLYCOGEN 



667. Glycogen is a carbohydrate which occurs in many cells, 

 both glandular and genital : it is found in both inter- and intra- 

 cellular positions, in the form of small areas of flocculent appear- 

 ance. For its study in a tissue or organ two methods should be 

 used : — (1) An iodine technique ; and (2) that of Best's carmine. 

 The specificity of the latter method has been questioned, and 

 both techniques must be used for comparison. 



668. Iodine Method. Fix tissue in Carnoy. or alcohol absolute, 

 4 parts ; acetic acid glacial, 1 part ; or in absolute alcohol ; or in 

 alcoholic fixatives not containing alcohol lower than a strength 

 of 90 per cent. It is better if the tissue is cut small. Fix for one 

 hour, then transfer for twenty-four hours or longer, in two changes 

 of absolute alcohol ; then xylol and paraffin v/ax. Fix sections 



