METHYLEN BLUE. 87 



take some four or five days, as sublimate is very little soluble 

 in xylol. Mount in balsam, or if sections be desired, imbed 

 in paraffin in the usual way. Sections should be fixed to the 

 slide with Schallibaum's collodion, and not with Mayer's 

 albumen, which discharges the colour. The preparations will 

 keep for several weeks, but the finer details are likely to fade 

 after a month. 



The times required for a ganglion of the ventral chain of a 

 crayfish are for (1) ten minutes, (2) fifteen minutes, (3) ten 

 minutes, (4) four or five days. 



FEIST, in the paper quoted above, recommends JOLIET'S 

 gum-glycerin imbedding method; but in most cases the 

 method of Parker will doubtless be preferable. 



Preparations preserved by the old methods (I do not know 

 whether it is the case with preparations preserved by Parker's 

 method) are extremely sensitive to the influence of light. 

 Diffused daylight is less injurious to them than the light con- 

 centrated on them by the illuminating apparatus of the 

 microscope during observation. Apathy finds that lamplight 

 is particularly injurious, especially the intense lamplight used 

 with high powers ; which he attributes partly to the yellow 

 rays, partly to the heat. 



120. Methylen-Blue Impregnation of Epithelia, Lymph- spaces, 



&c. (DOGIEL, Arch.f. mik. Anat., xxxiii, 4, 1889, p. 440, etseq.). Suitable 

 pieces of tissue (thin membranes by preference) are brought fresh into a 4 

 per cent, solution of methylen blue in physiological salt solution. After a few- 

 minutes therein they are brought into saturated solution of picrate of 

 ammonia, soaked therein for half an hour or more, then washed in fresh 

 picrate of ammonia solution, and examined in dilute glycerin. 



If it be wished only to demonstrate the outlines of endothelium cells, the 

 bath in the stain should be a short one, not longer than ten minutes in 

 general ; whilst if it be desired to obtain an impregnation of ground-sub- 

 stance of tissue so as to have a negative image of juice-canals or other spaces, 

 the staining should be prolonged to fifteen or thirty minutes, and it is 

 advisable to remove the endothelial covering of the objects operated on 

 before putting them into the stain. 



If it be desired to preserve the preparations permanently, they had better 

 be mounted in glycerin saturated with picrate of ammonia. (For an im- 

 provement in the method of preservation given in a later paper see supra, 



119.) 



The effect is practically identical (except as regards the colour) with that 

 of a negative impregnation with silver nitrate. 



121. MAYER'S (S.) Impregnation Methods (Zeit. f. wiss. 



