WITH THE MICROSCOPE. Ill 



alcohol. A grain of the colour, ten or fifteen drops of alcohol, and 

 an ounce of distilled water, make a dark red solution ; or the colour 

 may be boiled in water, allowed to cool, and then filtered. This 

 fluid colours tissues very readily. Many exceedingly delicate and 

 perfectly transparent textures, which are almost invisible in the 

 natural state, can be most satisfactorily demonstrated by the use of 

 this coloured fluid. The cilia of ciliated epithelium may be tinted 

 while they continue to vibrate. As the substance of the cell becomes 

 coloured, however, the action of the cilia ceases. Every kind of 

 cell wall, delicate membrane, and transparent tissue may be tinted 

 with these colours. 



Magenta has been recommended by Dr. Roberts for showing a 

 minute spot connected with the red blood corpuscles of man. (" On 

 peculiar appearances exhibited by blood corpuscles under the influ- 

 ence of solutions of magenta and tannin" Proceedings of the Royal 

 Society, vol. XII, p. 481, No. 55, April, 1863). The peculiar action 

 exerted by magenta and tannin upon the red blood corpuscles has 

 not yet been satisfactorily explained, but my friend, Dr. Hughes 

 Bennett, of Edinburgh, tells me that, with the aid of very high powers, 

 he has been able to demonstrate that the minute spot appearing after 

 the blood corpuscles have been soaked in magenta exhibits angles, and 

 he considers that it is in fact a minute crystal which has formed upon 

 the corpuscle. 



203. Blue Colours for staining'. Thiersch recommends the fol- 

 lowing fluid, the composition of which I take from Frey : 



Oxalic acid, i part. 



Distilled water, 22 parts. 



Indigo carmine, as much as the solution will take up. 



Another solution of oxalic acid and water in the same propor- 

 tion is required. One volume of the first solution is mixed with two 

 volumes of the last and nine of absolute alcohol. The mixture is 

 then filtered, and is ready for use. 



An anilin blue fluid may be made as follows : 



Soluble anilin blue, ^ grain. 

 Distilled water, i ounce. 

 Alcohol, 25 drops. 



This fluid is not acted upon by acids or alkalies. Frey strongly 

 recommends a fluid of this description as very useful for colouring 

 many tissues. 



204. Tannin. Although tannin does not colour animal membrane, 

 it alters its character to such an extent as to enable us to see many 



