MKTHYLEN BLUE. 229 



and quoted in his price list as " medicinisches Methylenblau," 

 and described 011 the label as " Anilin-blau, Methylen, 

 chemisch rein und chlorzinkfrei." It is therefore highly 

 desirable, when ordering methylen blue, to specify for what 

 purpose it is required. 



322. The Uses of Methylen Blue. As a histological reagent 

 it is used for sections of hardened central nervous tissue, in 

 which it gives a specific stain of inedullated nerves (post, 

 Part II). It is a valuable specific reagent for plasma-cells 

 (for which see also Part II). In stains a large number of 

 tissues intra vltam, with little or no interference with their 

 vital functions. And last, not least, it can be made to 

 furnish stains of nerve tissue, intercellular cement substances, 

 lymph spaces, and the like, that are essentially identical with 

 those furnished by a successful impregnation with gold or 

 silver, and are obtained with greater ease and certainty ; 

 with this difference, however, that gold stains a larger 

 number of the nervous elements that are present in a 

 preparation, sometimes the totality of them ; whilst methylen 

 blue stains only a selection of them, so bringing them more 

 prominently before the eye, and allowing them to be traced 

 for greater distances. So that in this respect methylen blue 

 behaves more like Golgi's chrome-silver impregnation. 



323. Staining in toto during Life. Small and permeable aquatic 

 organisms may be stained during life by adding to the water in which they 

 are confined enough methylen blue to give it a very light tint. If trans- 

 parent organisms be taken, they may be examined alive without further 

 manipulation at any desired moment, and will be found after a time to be 

 partially stained that is, it will be found that certain tissues have taken 

 up the colour, others remaining colourless. If now you put back the animals 

 into the tinted water and wait, you will find on examination after a sufficient 

 lapse of time that further groups of tissues have become stained. Thus it 

 was found by EHKLICH (Biol. Centralb., vi, 1886, p. 214; Abh. If. Akad. 

 Wiss. Berlin, February 25, 1885), to whom the principle of this method is 

 due, that on injection of the colour into living animals axis-cylinders of 

 sensory nerves stain, whilst motor nerves remain colourless. [The motor 

 nerves, however, will also'stain, though later than the sensory nerves.] It 

 might be supposed that by continuing the staining for a sufficient time, a 

 point would be arrived at at which all the tissues would be found to be 

 stained. This, however, is not the case. It is always found that the stained 

 tissues only beep the colour that they have taken up for a short time after 

 they have attained the maximum degree of celoration of which they are 



