BY R. VON LENDENPELD, PH.D. 25 



should be dipped in tlie solution if warm and left a short time if 

 cold. Tough organs can remain for some time in the solution. 

 Wilson (On Alcyonarians, Mittheilungen der zoologischen Station 

 in Neapel, 1884,) recommends to leave soft corals for several hours 

 in a wai-m concentrated solution of corrosive sublimate. For most 

 purposes this will be too strong. 



Picric acid solution or a mixture of it with sulphuric acid diluted 

 has been used by many with good results, so particularly Kleinen- 

 berg (Hydra). It is particularly good for staining nervous fibres 

 which are coloured yellow by it. 



Chromic acid or Bichromate of potassium in dilute solution is 

 used for brains to great advantage. 



Chloride of gold 1% solution colours nerve fibres and tissue cells 

 and the intercellular substance. 



Nitrate of silver is reduced by the intei'cellular substance and 

 eventually turns it black so that the limits of the cells can be made 

 clearly visible. 



Chloride of Palladium hardens the tissue and colours, muscular 

 fibre brown. Cloride of iron has also been reoommended for 

 hardening the tissue. 



Most metallic salts have some influence or other on the Proto- 

 plasm, and in every case the metal enters into combination with 

 it, changing its colour and making it hard. 



A specimen treated with one of these re-agents will stand 

 washing in distilled water without any perceptible change taking 

 place. 



Staining in Toto. 



The specimens should be stained, because the colour not only 

 makes certain parts more distinct, but also counteracts the 

 noxious after effects of the hardening^re-agents. Osmic acid, gold, 

 and other specimens, invariably commence to darken after some 

 months if they have not been stained. 



The specimens can either be stained when whole, or the sections 

 can be coloured. The staining in toto saves much trouble and 

 time, and is also advantageous, because the sections have not to be 



