210 CHAl'TEK XVI. 



345. Impregnation of Epithelia, Lymph-spaces, etc. (DoaiEL, 

 Arclt. -mill. Anal., xxxiii, 1889, p. 440 ct saq.). Suitable pieces 

 of tissue (thin membrane by preference) are brought fresh 

 into a 4 per cent, solution of methylen blue in physiological 

 salt solution (in the Encycl. mik. Technik, 1903, p. 827, 

 Dogiel gives the strength of the methylen blue as ^ to 1 per 

 cent.). 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 endo- 

 thelium 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-substance 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. 



If it be desired to preserve the preparations permanently, 

 they had better be mounted in glycerin saturated with picrate 

 of ammonia, or (Encycl., 1910, ii, p. 110) fixed with ammonium 

 molybdate and a trace of osmium. 



The effect is practically identical (except as regards the 

 colour) with that of a negative impregnation with silver 

 nitrate. 



S. MAYER (Zeit. wiss. Mik., vi, 1889, p. 422) stains tissues 

 for about ten minutes in a 1 : 300 or 400 solution of methylen 

 blue in 0'5 per cent, salt solution, rinses in salt solution, and 

 puts up in the glycerin-picrate of ammonia mixture given 

 343. The images are generally positive after injection of 

 the colour into the vascular system ; negative after immersion 

 of the tissues. 



TIMOFEJEW (Anat. Anz., xxxv, 1909, p. 296) impregnates 

 for 15 to 20 minutes in a solution of 1 : 3000 or 4000 strength, 

 fixes with a very weak solution of ammonium picrate in salt 

 solution, and puts up in a mixture of 50 c.c. glycerin, 50 c.c. 

 water, and 35 c.c. saturated solution of the picrate : or fixes 

 with ammonium molybdate of 8 per cent, and mounts in 

 balsam. 



346, Toluidin Blue or Thionin as succedanea of methylen 

 blue, HARRIS (Philadeyhia Hed. Journ., May 14th, 1898) 

 has found that there is no reaction of methylen blue that 



