CHAPTER XVI. . 189 



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. I 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. Lombardo, xxv, 1892 ; Zeit. wiss. 

 MiL, 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. Gland 

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

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

 corpuscles, elastic fibres, smooth muscle, striated muscle. There 

 are other elements that stain ih the living state, but not when the 

 staining is performed by simple immersion of intact animals in a 

 dilute staining solution in the manner we are. considering. Chief 

 amongst these are nerve-fibres and ganglion-cells, which remain 

 unstained in the intact organism. To get these stained, it is neces- 

 sary to isolate them sufficiently, as explained in the following 

 sections. 



340. Staining Nervous Tissue* during Life. It was made out by 

 EHRLICH (op. cit., last ) that by injecting a solution of methylen 

 blue into the vessels or tissues of living animals and shortly after- 

 wards 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 oxygen 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. DOGIEL, however (Arch. mik. Anat., 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 AP!THY (Zeit. wiss. Mik., ix, 1892, pp. 15 

 et seq.) that nerve-tissue can be stained after life has ceased. APATHY 



* See also p. 477. 



