MICROCHEMICAL TESTS 293 



well, § 699). Lead is precipitated as yellow lead chromate, 

 easily identifiable in sections. 



See also Macallum, Journ. Phys. Cambridge, xxii, 1897, p. 92 ; 

 INLvRFORi, Arch. Hal. Biol., xxx, 1898, p. 186. 



For Zinc see Mendel and Bradley, Amer. Journ. Phys., xiv, 1905, 

 p. 320. 



For Lime Salts see Grandis and Mainini, Arch. Ital. Biol., xxxiv, 

 1900, p. 75 ; ScHAFFER, Zeii. iviss. Zool., Ixxxix, 1908, p. 18 ; Leutert, 

 Enzyk. niikr. Technik, ii, p. 588 ; Stoeltzner, Arch. path. Anat., clxxx. 

 1905, p. 368 ; Macallum, Ergeb. Phys. Wiesbaden, vii, 1908, p. 612. 



For Potassium see Macallum, Journ. Phys. Cambridge, xxxii, 1905, 

 p. 95 ; Ergeb. Phys. Wiesbaden, vii, 1908, p. 600. 



For Guanin see Gl\como, Zeit. iviss. Mik., xxvii, 1910, p. 257. 



Concerning the microchemistry of the cell in general, see iurthev fourth 

 edition ; also Carnoy and Lebrun, La Cellule, xxii, 2, 1897, p. 194. ; 

 ZiMMERMANN, Die Morphologic u. Physiologie des Pflanzlichen Zellkernes, 

 Jena, 1896 (treats also of the animal cell) ; Haecker, Praxis u. Theorie 

 der Zellen und Befruchtungslehre, Jena ; Prenant, Journ. Anal. Phys., 

 xlvi, 1910, p. 34.3. For further references see Lison {op. cit.). 



677. Calcium. The following are two tests for this important 

 substance. Fix in acid-free alcohol or acid-free formol, bring 

 sections to 40 per cent, alcohol, and add 3 per cent, sulphuric acid 

 under the coverslip. Gypsum crystals will be formed if calcium 

 be present. The reaction takes place better in 40 per cent, 

 alcohol, as gypsum is somewhat soluble in water (Schuejeninoff, 

 Zeit. wiss. Micr., 1897). 



Cretin's Colour Test. This is an extremely sensitive test for 

 giving a specific blue colouration. Other metals give colours 

 with this test, for example, barium and strontium, green ; iron, 

 brownish-violet ; magnesium, rose ; silicon, yellow. 



Mix in a mortar 1 part of trioxymethylen and 2 parts of gallic acid. 

 For the test dissolve 0-25 grm. of the mixture in 5 c.c. of boiling distilled 

 water. To this boiling solution carefully add 0-5 c.c. of ammonia 

 18° B., shake till a straw-yellow colour appears. It is then ready, but 

 if it goes brown or rose colour it is useless, and in any case only lasts a 

 short time. Now remove the wax from sections with xylol, and wash 

 off the xylol with chloroform ; throw off excess chloroform, add the 

 gallic acid reagent and after ten or fifteen seconds, tip off excess reagent 

 and leave exposed to the air. The characteristic blue colour should 

 appear if calcium be present. 



This method is not easy, and like other complicated and ill-understood 

 microchemical reactions, requires practice (see Bull, histol. appl. No. 3, 

 1924). Masked calcium is detected best by microincineration (see 

 §§ 678, 1269) 



677a. Vitamin C. The researches which led to the elaboration 

 of a cytological technique for this vitamin were initiated by A, 

 Szent-Gyorgyi in 1927. Adrenal gland cortex treated with AgNOs 

 solution rapidly blackens. A crystalline substance, " hexuronic 

 acid," was isolated, and finally identified with vitamin C, partly 

 with the assistance of two Americans, C. King and W. A. 



