52 STAINING. 



93. The State of the Tissues to be Stained, It is generally 

 found that precise stains can only be obtained with carefully 

 fixed (i. e. hardened) tissues. Dead, but not artificially hard- 

 ened tissues stain indeed, but not generally in a precise 

 manner. Living tissue elements in general do not stain at all, 

 but resist the action of colouring reagents till they are killed 

 by them. 



Staining " intra vitam" Some few substances, however, 

 possess the property of staining living cells without greatly 

 impairing their vitality. Such are in very dilute solutions 

 cyanin (or quinolein),methylen blue, Bismarck brown, and, 

 under certain conditions, dahlia, and gentian violet, with per- 

 haps methyl violet and some others whose action is not yet 

 sufficiently established by experiment.* (The paper of Marti- 

 notti, Zeit.f. wiss. Mik., v, 3, 1888, p. 305, may be consulted 

 on this point.) 



As to the employment of these reagents, it may be noted 

 that they must be taken in a state of extreme dilution, and in 

 neutral or feebly alkaline solution acids being of course toxic 

 to cells. Thus employed, they will be found to tinge with 

 colour the cytoplasm of certain cells during life (never, so far 

 as I know, nuclear chromatin during life ; if this stain, it is 

 a sign that death has set in) . The stain is sometimes diffused 

 throughout the general substance of the cytoplasm, sometimes 

 limited to certain granules in it (which have been taken, 

 perhaps without sufficient reason, to be identical with the 

 granules of Altmann (Altmann's Studien iiber die Zelle, 1886). 

 Methylen blue has the valuable point that it is perfectly 

 soluble in saline solutions, and may therefore be employed 

 with marine organisms by simply adding it to sea- water. The 

 others are not thus soluble to a practical extent, but I find 

 that gentian and dahlia become so if a trace of chloral hydrate 

 O2 5 per cent, is amply enough be added to the saline solu- 

 tion. Any of these reagents may be rubbed up with serum, 

 or other " indifferent " liquid. 



Methylen blue may be fixed in the tissues, and permanent 

 preparations made, by treating for some hours with saturated 



* Congo, even in strong solution, is not toxic to some organisms, and stains 

 some structures (see Scholtz, Centralb. f. d. med. Wiss., 1886, p. 449 ; 

 also Journ. Roy. Mic. Soc., 1886, p. 1092). Living Rotifera are in part suc- 

 cessfully stained by it during life. 



