188 METHYLEN BLUE. 



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 EHRLICH (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 tissue^,would be found to 

 be stained. This, however, is not the case. It *s 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 " leucobase." Now living or recently dead 

 tissue elements are, or may be, both alkaline and very greedy of 

 oxygen, and thus act on the dye as reducing agents. 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 of 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 343. 



