158 CHAPTER XI. 



that is fully and perfectly alive. I am inclined to think 

 that the chief scientific value of the so-called vital or intra- 

 vitam stains may be found to lie in the fact that they may 

 furnish us with the means of distinguishing the living con- 

 stituents of a cell from the non-living ones, and even of 

 recognising amongst the living ones those that possess only 

 a relatively low or impaired degree of vitality. See on this 

 point (as on others connected with the theory of staining) 

 the work of FISCHER, quoted 200 A. 



Apart, however, from the question whether the elements 

 stained by the so-called " vital ' stains are truly living or 

 not, it must be conceded that this mode of treating living 

 cells has frequently a considerable measure of practical 

 utility. It often enables us to map out physiological or 

 morphological tracts that would otherwise be unrecognisable 

 or less readily recognisable in the living state. 



1 find methyleii blue, Congo red, neutral red, gentian and 

 dahlia added to indifferent liquids, extremely useful in the 

 examination of tissue-cells. Quinolein and Bismarck brown 

 are well-known aids to the study of Infusoria. Methyleu 

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

 extremely important reagent (see post, Chap. XVII) . Accord- 

 ing to my experience, methyleii blue is the most generally 

 useful of these stains. It has (with Bismarck brown, Congo 

 red and neutral red) the valuable point that it is sufficiently 

 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 ample enough be added to the saline 

 solution. Any of these reagents may be rubbed up with 

 serum, or other " indifferent " liquid. 



Methyleii blue may be fixed in the tissues, and permanent 

 preparations made, by one or other of the methods described 

 in Chap. XVII. Bismarck brown stain s may be fixed with 0' 2 

 per cent, chromic acid or with sublimate solution. (MAYER), 

 or 1 per cent, osmic acid (LoiSEL, Joitru. <!<' l\\tnd. et de la 

 Pliys., 1898, No. 2, p. 212- a work that contains a good deal 

 of information on the subject of intra-vitam stains), and the 

 preparations may be stained with safraniu, care being taken 

 not to expose them too long to the action of alcohol. 



