METHYLEN BLUE. 201 



blood, blood parasites, and similar objects. For all of these 

 see the respective sections in Part TI. Further, it stains a 

 large number of tissues hitra vitam, with little or no inter- 

 ference 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 silvei', 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. These two uses form the subject of 

 this chapter. 



339. 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. After a time they will be found 

 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 after a further lapse of time that further 

 groups of tissues have become stained. Thus it was found 

 by Ehelich {Biol. Centralb., vi, 1886, p. 214; Alh. k. Almd. 

 Wiss. Berlin, February 25th, 1885) 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 keep the colour that they have taken up 

 for a short time after they have attained the maximum 

 degree of coloration of which they are susceptible, and then 

 begin to discharge the colour even more quickly than they 

 took it up. According to Ehelich this decoloration is 

 explained as follows : methylen blue, on contact with reduc- 

 ing agents in alkaline solution, can be reduced to a colourless 



