156 CHAPTER XI. 



stitueiits of the tissues with the chemical elements brought 

 to them by the fixing agent, as seems to happen when such 

 a fixing agent as chromic acid is employed the compounds 

 in question being probably chiefly metal albuminates. 

 These considerations will serve to show to how great an 

 extent the quality of a stain is dependent on the nature of 

 the previous treatment the tissues have undergone. 



200 a. The Molecular Processes involved in Staining. The 

 question whether the phenomena of staining and of industrial dyeing are 

 of a chemical order, as held by some, or of a purely physical order, as held 

 by others, is outside the province of this book. See the elaborate discussion 

 of the subject in FISCHER'S Fixirung, Fdrbung und Ban des Protoplasmus, 

 Jena, G. Fischer, 1889. 



201. Staining " intravitam." Some few substances possess 

 the property of staining or rather, tiiigeing living cells 

 without greatly impairing their vitality. Such are in very 

 dilute solutions cyanin (or quinolem), methylen blue, 

 Bismarck brown, anilin black, Congo red, neutral red, Nile 

 blue, and, under certain conditions, dahlia and eosin, gentian 

 violet, with perhaps methyl violet, and some others whose 

 action is not yet sufficiently established by experiment. 



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

 that they must be taken in a state of considerable 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 can see, 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, in some cases certainly without sufficient 

 reason, to be identical with the granules of Altmann 

 (Altmann's Studien uber die Zelle, 1886). 



It has been asserted by some observers that the nucleus 

 may be stained during the life of the cell by means of 

 Bismarck brown, v Congo red, methylen blue, neutral red, Nile 

 blue, v and safranin/ But it is by no means clear from the 

 statements of these writers that the coloration observed by 

 them is localised in the chromatin of the nucleus. It would 



