COAL-TAR CHROMATIN STAINS. 205 



with neutral alcohol, or (FLEMMING, Zeit. f. wiss. Mik., 1, 

 1884, p. 350) acidulated alcohol, as directed for safranin. 

 BIZZOZERO (Zeit. f. iciss. Mik., iii, 1, 1886, p. 24) stains in a 

 solution borrowed from that of EHRLICH for bacteria, and 

 consisting of 



Gentian violet . ... 1 part. 



Alcohol . . . . .15 parts. 



Anilin oil . . . . 3 



Water 80 



The complicated chromic-acid differentiation process recom- 

 mended by him appears to me quite superfluous. 



In some cases it may be useful to employ the method 

 devised by GRAM for the differentiation of bacteria in tissues 

 (Fortschr. d. Medicin., ii, 1884, No. 6 ; British Med. Journ., 

 Sept, 6th, 1884, p. 486; Journ. Roy. Hie. Soc. [N.S.], iv, 

 1884, p. 817). 



In Gram's method the sections ar treated, after staining, 

 with a solution composed of 



Iodine ..... 1 gramme, 



Iodide of potassium . . 2 grammes, 



Water .... 300 



for two or three minutes, until they become black. They 

 are then differentiated with neutral alcohol, until they turn 

 grey, and are then finally differentiated with clove oil. 



By this process, in resting nuclei the nucleoli alone are 

 stained, or the chromatin if stained is pale ; in dividing 

 nuclei the chromatin is stained with great intensity, being 

 nearly black in the equatorial stage. 



Gentian violet is an exceedingly powerful stain, quite as 

 precise as safranin, to which it is perhaps even preferable for 

 much work with very thin sections (thick sections with 

 closely packed nuclei may easily come out too dark). It 

 lends itself well to double-staining with red or yellow plasma 

 stains. 



The stain keeps well if the preparations be not unduly 

 exposed to light. 



Gentian violet in acid solution stains the nuclei of fresh tissues, and dis- 

 solved in indifferent media is sometimes very useful for staining intra vitam 

 (see 201). 



HERMANN (Arch. mik. Anat., xxxiv, 1889, p. 58) first stains for twenty- 

 four hours or more in safranin, differentiates incompletely with .alcohol, 



