754 SUMMARY OF CUREENT RESEARCHES RELATING TO 



For the same purpose is also used a solution of iodine in water or 

 in alcohol (tincture of ioiliue), of different strengths, and in glycerin, 

 to which is added a small quantity of iodide of potassium. 



Alkalies. — Treated with nitric acid, then with ammonia or potash 

 dissolved in water, the pr(jtoplasm is coloured yellow ; it assumes a 

 dark violet tint when the action of the alkali has been preceded by 

 thit of a concentrated solution of sulphate of copper, followed by 

 washing in water. The colouring can be better judged of by the in- 

 troduction of the alkali in a slow current between the slide and the 

 cover-glass, the liquid being sucked through by means of filtering- 

 paper. 



Hydrochloric acid. — The protoplasm becomes pink or slightly 

 violet'^when left for a few seconds in boiling hydrochloric acid. 



Sulpliuric acid and Sugar. — The preparations are treated with 

 sulphuric acid, and then washed in distilled water, so as to free them 

 as much as possible from the acid ; then, Ixjtween the two glasses in- 

 closing the objects, is passed a current of concentrated solution of 

 su<^ar ; all the protoplasm becomes pink or violet. In this operation 

 the difficulty lies in exactly regulating the time of the immersion in 

 the sulpliuric acid. When too short, it is useless : when too long, it 

 destroys the whole of the protoplasm. Generally spe iking, when 

 English concentrated acid is used, the action must be stopped as soon 

 as the protoplasm becomes very slightly pink. 



Acetic acid and Cochineal. — To a solution of cochineal in alc:)hol 

 at GO^ C, 2 per cent, of acetic acid must be added. This reagent gives 

 a pinkish or violet tint to the protoplasm. 



Carmine. — The carmine is dissolved in ammonia, and the solution 

 allowed to evaporate in the air, so that it may be us little alkaline as 

 possible. In these conditions it colours the protojilasm red. 



Anilin colours. — The use of anilin colours as reagents for proto- 

 plasm is of recent date. It gives very good results. Unfortunately 

 the reactions differ according to the origin of the products, wliich are 

 not identical in all makes. Purple, blue, and yellow are used prin- 

 cijially in alcoholic solution. Anilin violet dissolved in alcohol is 

 particularly valuable, because it colours the principal mass of the 

 protoplasm a blue violet, whilst under its influence the nuclei, ternary 

 substances, gums, and amylaceous substances become reddish.* 



Koch f made use of anilin-brown and hematoxylin to colour 

 bacteria, and photograph them more, easily ; these may then be pre- 

 served in glycerin with the addition of potassium acetate; in this 

 solution the colouring is ju'eserved. The same precaution must be 

 taken when the bacteria are treated with methyl-violet or violet of 

 Paris. 



This reagent in alcoholic solution has been of great use to the 

 author in the study of micro-organisms. When very concentrated, it 

 may be used for the vibratile cilia, which are invisible when they are 

 not coloured, but can be seen very distinctly in this liquid. The 

 fundamental protoplasm being easily stained with this substance, it is 



♦ Poulsen, loc. cit. p. 48. 



t OoLd, 13titr. z. Biol, iler Til., ii. p. -lOG. 



