METHYLEN BLUE 191 



animals into the tinted water and wait, you will lind after a further 

 lapse of time that further groups of tissues have beeome stained. 

 Thus it was found by Ehrlicii {Biol. Centralb., vi, 1886 p. 214) ; 

 Abh. k. Akad. 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 Ehrlich this decoloration is explained as 

 follows : methylen blue, on contact with reducing agents in 

 alkaline solution, can be reduced to a colourless body, its " leuco- 

 base." Living tissues readily reduce methylen blue. The 

 leucobase thus formed is easily reoxidised into methylen blue by 

 oxidising substances, or acids, or even by the mere contact of air — 

 which latter property is taken advantage of in practice. 



It follows that a total stain of all the tissues of a living intact 

 organism can hardly be obtained under these conditions, but 

 that a specific stain of one group or another of elements may be 

 obtained in one or two ways. If the tissue to be studied be one 

 that stains earlier than the others, it may be studied during life 

 at the period at which it alone has attained the desired intensity 

 of coloration. If it be one that stains later than the others, it 

 may be studied at the period at which the earlier stained elements 

 have already passed their point of maximum coloration and have 

 become sufficiently decoloured, the later stained ones being at a 

 point of desired intensity. Or the observer may fix the stain in 

 either of these stages and preserve it for leisurely study by means 

 of one of the processes given, § 382. 



The proper strength of the very dilute solutions to be employed for 

 the staining of living organisms must be made out by experiment for 

 each object. We think the tint is practically a sufficient guide, but it 

 may be stated that when in doubt a strength of 1 : 100,000 may be 

 taken, and increased or diminished as occasion may seem to require. 

 ZojA {Rendic. R. 1st. Lonibardo, xxv, 1892 ; Zeit. iviss. Mik., ix, 1892, 

 p. 208) finds that for Hydra the right strength is from 1 : 20,000 to 

 1 : 10,000. 



The stain is capricious. It is not possible to predict without trial 

 which tissues will stain first in any organism. The stain penetrates very 

 badly, which is no doubt one cause of its capriciousness. (iland cells 

 generally stain early ; then, in no definable order, other epithelium cells, 

 fat cells, plasma cells, " Mastzellen," blood and lymph corpuscles, 

 elastic fibres, smooth muscle, striated muscle. There are other elements 

 that stain in the living state, but not when the staining is performed by 



