METHYLEN BLUE. 203 



remain unstained in the intact oryanisni. To get these 

 stained, it is necessary to isolate them sufficiently, as explained 

 in the following sections. 



340. Staining Nervous Tissue during Life. — It was made out 

 by Ehelich {op. cit., last §) that by injecting a solution of 

 methylen blue into the vessels or tissues of living animals 

 and shortly afterwards cutting out and examining small 

 pieces of their tissues, these will be found to be intensely 

 stained in some of their elements (chiefly nervous). If the 

 tissues are mounted under a cover-glass, the stain will fade 

 in a short time ; but if the cover-glass be removed, so that 

 o^y&^n can have access to the tissues, the stain will be 

 restored, as explained last §. The chief elements stained 

 in this way are peripheral nerves, and amongst these more 

 especially axis-cylinders of sensory nerves. 



Ehrlich held that the stain so obtained is a product of a 

 vital reaction of the tissues, and that it cannot be obtained 

 with dead material. Dogibl, however {Arch. mik. Anaf., 

 XXXV, 1890, pp. 305 et seq.), found that muscle nerves of 

 limbs of the frog could be stained as much as from three to 

 eight days after the limbs had been removed from the animal. 

 He concludes, indeed, that the reaction shows that the nerves 

 were still living at that time. But it seems more natural to 

 conclude with Apathy {Zeit. wiss. Mik., ix, 1892, pp. 15 

 et s(q.) that norve-tissue can be stained after life has ceased. 

 Apathy has directly experimented on this point, and sums up 

 the necessary conditions as follows : The tissue need not be 

 living, but must be fresh ; nothing must have been extracted 

 from it chemically, and its natural state must not have been 

 essentially changed by physical means. For example, the 

 tissue must not have been treated with even dilute glycerin, 

 nor with alcohol, though a treatment for a short time with 

 physiological salt solution is not very hurtful ; it must not 

 have been coagulated by heat. Michailow {ibid., xxvii, 

 1910, p. 7) prefers tissues that have lain from one and a half 

 to two hours after the death of the subject in Ringer's salt 

 solution. 



As above explained, the primary stain obtained by injecting 

 methylen blue, or immersing tissues in it, only lasts a 

 very short time. In order to get it to last long enough for 



