232 THE MICROSCOPE 



is easily removed by prolonged washing in water (Ranvier). 

 Tissues easily stain in picro-carmine. Sometimes one part of 

 water is added to two parts of the saturated solution. It is used 

 to decalcify the bones, and for the salivary glands and pancreas. 



Kleinenberg's Picric Acid is a modification of the above. To 

 I GO cc. of a cold, saturated, aqueous solution of picric acid add 2 

 cc. of strong sulphuric acid, which throws down a yellow precipi- 

 tate. Filter, and to the filtrate add 300 cc. of distilled water. 

 This solution is most valuable for foetal tissues, and especially for 

 early embryos. It produces its effects in from three to ten hours. 



Silver Nitrate is useful in all cases when it is required to 

 demonstrate the flat tesselated or endothelial cells of serous mem- 

 branes. This salt is taken up by the intercellular substance when 

 fresh, and reduced as a black precipitate under the action of light, 

 and so maps out the cells in black lines. The tissue must be 

 perfectly fresh ^ and placed directly after removal from the body in 

 a '5 per cent, or '25 per cent, solution for from ten to fifteen 

 minutes ; then washed carefully in distilled water, and exposed to 

 the light in glycerine diluted with three times its bulk of distilled 

 water. Silver is also used to stain nerve-fibres. To prepare the 

 solution: — Finely powder in a mortar 5 grammes (i drachm 17 

 grains) of crystallised nitrate of silver ; add gradually 1,000 cc. 

 (35 ounces 2 drachms 20 minims) of cold distilled water. When 

 the salt has dissolved, preserve in a dark-stoppered bottle and keep 

 in a dark cupboard. The use of silver nitrate in bringing in view 

 the cell-spaces of the cornea will be alluded to later on. Sections 

 may be mounted in Canada Balsam. 



Ammonium-molybdate produces a bluish-grey general stain, 

 which acts well as a base for double stairiing ; a 5 per cent, 

 solution in water may be used, and the specimens should be 

 exposed to the light for twenty-four hours. The salt is expensive, 

 and the advantages of its use not very marked. 



Palladium chloride, in solutions varying from i per cent, to 5 

 percent., is occasionally used. We simply mention it as it has 

 the same effect as gold chloride in hardening and staining tissues. 

 It is very expensive, and, unfortunately, with many tissues, as 



