METHYLEN BLUE. 75 



The observer will do well to assure himself that he has_ 

 obtained a genuine iodine green, other coal-tar greens being 

 sometimes palmed off on the unwary purchaser for iodine 

 green. The presence of iodine may be tested in the following 

 way : A little of the solid colouring matter is treated with 

 sulphuric acid, and a few small fragments of bichromate of 

 potash are added ; the iodine, if present, escapes in the form of 

 violet vapours. It may also be demonstrated by means of 

 chloroform or sulphide of carbon. 



The colour may be obtained of excellent quality from C. A. 

 F. KuhlbaumV Chemische Fabrik, Berlin, S.O. (Zool. Anz., 

 No. 130, 1883, p. 56.) 



122. Thiophen Green (Thiophengriin,) (KRAUSE, Intern. Monatsschr. 

 f. Anat., &c., iv. 1887, Hft. 2). Krause finds that the double zinc-salt of 

 Thiophen green prepared by V. Meyer is useful for double staining with 

 carmine. Sections should be stained (after borax carmine) for a few minutes 

 in a concentrated aqueous solution, and be well washed out with absolute 

 alcohol. 



123. Anilin Green has a special affinity for mucus gland 

 cells. We shall return to this subject in the chapter on glands. 



124. Picro-anilin Green (TAFANI; see Journ. de Microgr., 1878, p. 

 82). (Mixture of anilin blue and picric acid solution.) 



125. Anilin Blue. Used alone, without special precautions, 

 this is a diffuse stain hardly to be recommended at the present 

 time. See, however, the method of HEIDENHATN, Arch.f. mik. 

 Anat. vi, 1870, p. 404. It is useful for double-staining. 



126. Parma Blue (Toluidin Blue, Lichtblau). A fast stain either 

 in aqueous or balsam mounts, was much recommended by FEET (Archf. mik. 

 Anat., 1868, p. 346). An aqueous solution of O'l per cent, will stain tissues 

 sufficiently in a few minutes. 



127. Methylen Blue, This is an important colour. It is 

 used for staining organisms during life (see 93). It has a 

 special affinity for sensitive nerve-endings, which it stains 

 during life. It is used alone or combined with other re- 

 agents, for staining nerve centres (post, Part II). And it 

 possesses the property of washing out certain other anilins, 

 with which it gives valuable double-stains (ante, 98, and post, 

 Chapter XIII). 



