56 t STAINING. 



1886, p. 449; also Journ. Roy. Mic. 8oc., 1886, p. 1092). 

 Living Rotifera are in part successfully stained by it during 

 life. (The paper of Martinotti, Zeit.f. wiss. Mik., v. 3, 1888, 

 p. 305, may be consulted on this subject.) 



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 uberdie 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 

 0*25 per cent, is amply enough be added to the saline 

 solution. 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 one or other of the methods described 

 in Chap. IX. Bismarck brown stains may be fixed with 0*2 

 per cent, chromic acid, and the preparations may be stained 

 with safranin, care being taken not to expose them too long 

 to the action of alcohol. 



I may say that personally I have found gentian, dahlia, and 

 methylen blue, added to indifferent liquids, extremely useful 

 in the examination of tissue-cells. Quinolei'n and Bismarck 

 brown are well-known aids to the study of Infusoria. Me- 

 thylen blue has a specific affinity for sensory nerves, and is an 

 extremely important reagent (see post, Chap. IX, and Part II). 



94. Choice of a Stain. The following may be recommended 

 with confidence for general work : For sections, Fie mining's 

 method, with safranin or gentian for a single stain, or Hen- 

 neguy's permanganate modification of the same (Chap. VIII), 

 and the same with hsematoxylin ( 106), or Flemming's 



