:n.X] 



REAGENTS AND THEIR PREPARATION 



363 



584. Normal liquids. A normal liquid or fluid is one which 

 does not injure or change a fresh tissue put into it. The perfect 

 normal fluids for the tissues of any animal are the fluids of the body 

 (lymph and plasma) of the animal from which the tissue is taken. 

 The lymph or serum of one species of animal may be far from normal 

 for the tissues of another animal (see also 499). 



The commonly used artificial normal fluid is a solution of common 

 salt (sodium chlorid) in water, the 

 strength varying from -^ to T V per 

 cent. As indicated above, this normal 

 salt or saline solution is emproyed in 

 diluting dissociating liquids ( 499) . 



585. Paraffin wax. A histologic 

 laboratory requires two grades of par- 

 affin for ordinary work. These are hard 

 paraffin, melting at about 54 centi- 

 grade, and a softer paraffin melting at 

 about 43 centigrade. Usually a mix- 

 ture of equal parts answers very well. 

 It is economical for a laboratory to buy 

 the paraffin wax in cases of about 100 

 kilograms. 



All paraffin for imbedding and section- 

 ing should be filtered through two thick- 

 nesses of filter paper. For this, use a 

 metal funnel, heat the paraffin very hot in a water bath, and then 

 heat the funnel occasionally with a Bunsen flame. The warmer the 

 room the easier it is to filter the paraffin. 



Filter the paraffin into small porcelain pitchers. If the paraffin 

 oven has a compartment large enough, it is well to keep one of the 

 pitchers in the oven; then the paraffin remains melted and is ready 

 for use at any time. 



586. Picric-alcohol. This is an excellent hardener and fixer 

 for almost all tissues and organs. It is composed of 500 cc. of water 

 and 500 cc. of 95 % alcohol, to which 2 grams of picric acid have been 

 added. (It is a J % solution of picric acid in 50 % alcohol.) It acts 



FIG. 214. SPECIMEN JAR 

 WITH CLAMP. 



