NUCLEAR STAINS WII'II COAL-TAIi DVJiia. 179 



In some cases it may be useEul to employ the metliod 

 devised by Gram for the differentiation of bacteria in tissues 

 {h\>rt.<schr . d. ]\[edicin., ii, 1884^ No. 6; Biitiah Med. Journ., 

 Sept. 6th, 1884, p. 486; Journ. Roy. Mic. Soc. [N.8.], iv, 

 1884, p. 817). In this the sections are treated, after stain- 

 ing, 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. 



The stain keeps well. It is more or less dichi-oic, possibly 

 owing to the fact that the dye is not a pure substance, but 

 a mixture of " Krystallviolett " and methyl violet. 



Heemann" (Arch. mih. Anat., xxxiv, 1889, p. 58) first stains for twenty- 

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

 then stains for three to five minutes in tlie anilin- water gentian solution, 

 treats with the iodine solution for one to three hours, and finally 

 differentiates with absolute alcohol. 



288. Thionin. — The hydrochloride of thionin, or violet of 

 Lauth, is a colour chemically nearly allied to methylen blue. 

 Its action is so selective from the first that it may almost be 

 considered to be a progressive stain. If you stain for only 

 a short time (a few minutes) in a concentrated aqueous 

 solution, hardly anything but the chromatin will be found 

 to be stained. If the staining be prolonged, plasmatic 

 elements will begin to take up the colour. After a short 

 stain no special differentiation is required ; all that is 

 necessary is to rinse with water, dehydrate, and mount. 

 After a strong stain you differentiate with alcohol in the 

 usual way, with this advantage, that the stain is so highly 

 resistant to alcohol that there is no risk whatever of over- 

 shooting the mark ; the stain will not be more extracted in 



