METHYLEN BLUE. 233 



rated (i. e. about 4 per cent.) solution into the vena cutanea 

 magna of frogs, and removed the organ to be investigated 

 after the lapse of an hour. BIEDERMANN (Sitzb. d. A'. Ah ad. 

 Wiss. Wlen, Math. Nat. CL, 1888, p. 8) injected 0'5 to 1 c.c. 

 of a nearly saturated solution in 0'6 per cent, salt solution 

 into the thorax of crayfishes, and left the animals for from 

 two to four hours before killing them. S. MAYER (Zeit.f. 

 wiss. Mik-., vi, 4, 1889, p. 423) took a strength of 1 : 300 or 

 400 of 0'5 per cent, salt solution. This can be introduced 

 into the system either by means of a syringe or other inject- 

 ing apparatus, or by auto-injection through the heart. Even 

 rabbits support this operation if artificial respiration be main- 

 tained. The solutions of RETZIUS are of the same strength. 

 But the tendency of more recent practice is decidedly towards 

 the employment of weaker solutions. APATHY (Zeit.f. in*.?. 

 J//A-., ix, 1, 1892, pp. 25, '2Q. et *eq.) finds that it is not only 

 superfluous, but positively disadvantageous, to take solutions 

 stronger than 1 : 1000. 



For staining by immersion similar solutions to those used 

 for injecting may be employed, but they should, if anything, 

 be still weaker. DOGIEL (Arch. f. mik. Anat., xxxv, 1890, 

 p. 305 ; Zeit.f. -iriss. Mik., vii, 4, 1891, p. 509) places objects 

 in a few drops of aqueous or vitieous humour, to which are 

 added two or three drops of a -^ to T * T per cent, solution of 

 methylen blue in physiological (0'75 percent.) salt solution, and 

 exposes them therein to the air. In thin pieces of tissue the 

 stain begins to take effect in five or ten minutes, and attains 

 its maximum in from fifteen to twenty minutes. For thicker 

 specimens retina, for instance several hours maybe neces- 

 sary, the preparation being kept just moist by occasional 

 treatment with a drop or two of indifferent liquid or methylen 

 blue solution, added by turns. The reaction is quickened by 

 putting the preparations into a stove kept at 30 to 35 ('. 

 EOUGET (Compt. Rend., 1893, p. 802) found it useful to 

 modify the procedure of Dogiel by employing a 00'5 per 

 cent, solution in 0'6 per cent, salt solution (for muscles of 

 Batrachia). ALLKN (Quart. Journ. il/y'c. 8ci., 1894, pp. 461, 

 483) takes for embryos of the lobster a solution of O'l per 

 cent, in 0'75 per cent, salt solution, and dilutes it with 15 

 to 20 volumes of sea water. 



