METHYLEN BLUE. 239 



(Arch. mik. An at., xlix, 1897, p. 772; liii, 1898, p. 237; 

 and Zeit.f. wis*. Zool., Ixvi, 1899, p. 361). 



PLESCHKO (Anat. Am., xiii, 1897, p. 16) fixes with picrate of ammonia, 

 and then puts into 10 per cent, formol for a few days. 



HARRIS (Philadelphia Medical Journ., May 14th, 1898) 

 after staining rinses with water, and brings the specimens 

 into a saturated solution of either ferrocyanide or ferri- 

 cyanide of potassium which has been cooled to within a few 

 degrees of zero (a trace of osmic acid may be added to prevent 

 maceration). They remain therein for three to twenty-four 

 hours, and are then washed in distilled water for an hour, and 

 are dehydrated in absolute alcohol kept at a low temperature, 

 cleared in xylol or cedar oil, and imbedded in paraffin. 



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

 etc. (DOGIEL, Arch.f. mik. An at., xxxiii, 4, 1889, p. 440, et seq.). 

 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 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, 

 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 improvement in the method of pre- 

 servation given in a later paper see supra, 328.) 



The effect is practically identical (except as regards the 

 colour) with that of a negative impregnation with silver 

 nitrate. 



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

 vi, 4, 1889, p. 422). MAYER'S experiments cover much the 



