STAINING ANIMAL SECTIONS. 265 



In place of alcohol, methylated spirit may be used if 

 desired. 



The chromo-lithograph forming the frontispiece to this 

 work, illustrates very clearly the value of the foregoing 

 methods. The four outside figures are specimens of 

 double-staining in carmine and green, some of the admi- 

 rable specimens of Mr. Ward, of Manchester, while the 

 centre figure is a representation of the slide sent by Mr. 

 Stiles, of Doncaster, to illustrate his paper on picro-carmine 

 staining in 'The Northern Microscopist.' 



Histological (animal) staining differs somewhat from the 

 foregoing, many processes having been devised to strikingly 

 differentiate the tissues. In 1876, Dr. Elizabeth Hoggan 

 described a process with iron and pyrogallic acid as 

 follows :* 



" The colouring agents required are a one or two per cent, 

 solution of perchloride of iron in alcohol, and an alcoholic 

 solution of pyrogallic acid of similar strength." 



The section or membrane to be stained is first treated 

 for a short time with alcohol, the iron solution filtered 

 upon it, and then poured off after a couple of minutes. 

 The pyrogallic solution is then filtered upon it, and 

 when the desired depth of staining has been obtained, 

 the tissue is washed and mounted in any of the usual 

 ways. 



The nuclei and nucleoli are by this means coloured 

 black, and the cell-substance coloured more or less. A 

 bluish tint may be imparted by washing in alkaline water 

 or in water highly charged with carbonate of lime. 



Osmic acid has been frequently recommended for 



staining animal tissues black, but it is doubtful whether 



anything is gained by its use. Dr. G. Brosicke, of Berlin, 



advises a mixture of osmic and oxalic acids for this 



* ' Journal of the Quekett Club,* iv. p. 180. 



