2So PREPARATION OF REAGENTS [ CH. IX 



chlorid deteriorate, hence it is better to imbed them soon after they are fixed. 

 Crystals of mercury are removed from the sections by the use of iodized 

 alcohol (I 413). 



417. Alkaline Methylene Blue. Methylene blue 2 grams ; 95% or abso- 

 lute alcohol 50 cc. ; distilled water 450 cc.; \% aqueous caustic potash 5 cc. 

 This stain works best after a mercuric fixer or a fixer containing mercuric 

 chlorid, like Zenker's fluid. 



\ 418. Muller's Fluid. Potassium dichromate 2^ grams; sodium sul- 

 phate, i gram ; water 100 cc. This is one of the oldest fixers. It must act a 

 long time, two weeks to 10 or 12 weeks. This longer time is for nervous tissue 

 to be stained for the myelin. Lately this fixer has been combined with mer- 

 cury (see Zenker's fluid below). Before putting the tissue into 67% alcohol it 

 is washed out in running water for 24 hours. 



Muller's Fluid 10 cc ; normal salt solution 90 cc., forms an excellent disso- 

 ciator for epithelia, etc. ( 399). 



\ 419. Neutral Red. This is used especially for staining living animals. 

 It is used in very weak solutions : -fa gram red ; 1000 cc. of water. Put a few 

 cubic centimeters of this solution into the vessel containing the live animal, 

 or animals. Infusoria stain quickly 10 to 20 minutes or less. Vertebrates 

 may require a few days. Try it on infusoria by adding a drop of the red to 

 several drops of the infusion containing the infusoria. Be sure that there are 

 many animals present. Watch them under the microscope and the color will 

 be seen appearing in the granules of the infusoria. Then one may cover and 

 study with a high power. 



\ 420. Nitric Acid, H-NO... This is employed for dissociation (Nitric 

 acid Dissociator, Water 80 cc.. ; Nitric acid 20 cc.); as a fixer, especially for 

 chick embryos in the early stages (Water 90 cc.; Nitric acid, 10 cc. ), and as a 

 decalcifier (Nitric acid 3 cc. ; 67% alcohol 100 cc.). 



'',. 421. 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. 



The commonly used artificial normal fluid is a solution of common salt 

 (sodium Chlorid) in water, the strength varying from ^ to ^ per cent. Aa 

 indicated above, this normal salt or saline solution is employed in diluting 

 dissociating liquids (| 399). 



\ 422. Paraffin Wax. A histologic laboratory requires two grades of 

 paraffin for ordinary work. These are hard paraffin, melting at about 54 

 centigrade, and a softer paraffin melting at about 43 centigrade. Usually a 

 mixture of equal parts answers very well. It is economical for a laboratory to 

 buy the paraffin wax in cases of about 200 pounds. 



All paraffin for imbedding and sectioning should be filtered through two 

 thicknesses of filter paper. For this, use a metal funnel, heat the paraffin very 



