MS 32.0 



METAL STAINS 



565 



back to expose the sciatic nerve. If this 

 operation is skilfully clone there will be no 

 bleeding. 



Before removing the nerve it is desirable 

 to have some form of stretcher which may 

 be used to keep it straight during the 

 process of fixation. The simplest method 

 is to use the nerve as the string of a bow, 

 the bow itself being made either from a 

 fine sliver of bamboo, or from some thin 

 plastic which will apply the required ten- 

 sion. The author prefers the small stiffen- 

 ing devices which are sold for insertion 

 into the collars of men's shirts. These are 

 usually about 2 inches long by Js of an 

 inch wide, and may be cut down the 

 middle with a sharp knife to make two 

 bows from each. The selected piece is laid 

 down flat alongside the nerve, which has 

 been freed from the fascia with some 

 blunt-pointed instrument, and one end of 

 the bow tied firmly to the nerve with a 

 piece of surgical silk. The bow is then bent 

 very slightl.y — from li to Ke of an inch, 

 given sufficient tension — and the other 

 end similarly lashed to the nerve with 

 surgical silk. The required piece of nerve 

 is then severed and lifted out, using the 

 bow as a handle, and transferred to about 

 100 milliliters of fixative, preferably being 

 suspended in the fixative by a thread tied 

 around the bow. In the fixative recom- 

 mended with this technique, from 24 to 48 

 hours are sufficient. 



The usual precautions with regard to 

 the purity of the reagents employed and 

 chemical cleanliness of the glassware must 

 be observed in staining the sections. 

 Staining and washing is most conveniently 

 done in rectangular jars, and it is best to 

 use a single jar for all the staining, fixing, 

 and toning operations, though the usual 

 jars of xylene and alcohols will be required 

 for deparaffinizing and dehydrating. The 

 solutions required in order of their use 

 are: 



A. 5% silver nitrate. This presents no 

 difficulty in preparation provided that re- 

 agent grades of silver nitrate and triple- 

 distilled water are employed in chemically 

 cleaned glassware. 



B. 0.2% silver protein. The simplest 

 way to dissolve the silver jM'otein is to 

 sprinkle the dry powder on the surface of 



the water. The mixture should not be 

 stirred, Init the powder should be allowed 

 to drop through the water of its own 

 weight. When no further silver protein is 

 left on the surface, the material may be 

 stirred rapidly and then placed on one side 

 for use. 



C. Davenport's developer, the formula 

 for which is given under AIMS 21.1 Daven- 

 port, Windle, and Rhines 1947 in Chapter 

 24. To prepare the solution .5 grams of 

 sodium sulfite are dissolved in 100 milh- 

 liters of water. When solution is complete, 

 1 gram of hydroquinone is added and al- 

 lowed to dissolve completely before adding 

 a J^^-gram of potassium metaborate, which 

 is commercially available under the trade 

 name of Kodalk. 



D. 0.2% gold chloride. 



E. 0.4% oxalic acid. 



F. 5% sodium thiosulfate. 



The technician should now have in 

 front of him two jars of xylene, one jar of 

 absolute alcohol, one jar of 95% alcohol, 

 one jar of 70% alcohol, one jar of 50% al- 

 cohol, one jar of distilled water, and one 

 jar of 5% silver nitrate. He should also 

 have available in beakers a sufficient 

 quantity of the silver protein solution, the 

 developer, the gold chloride, the oxalic 

 acid, and the sodium thiosulfate to fill one 

 of the jars. It is to be presumed that the 

 nerve has been sectioned by the ordinary 

 paraffin technique and the sections, of a 

 thickness of from eight to ten microns, 

 mounted on glass slides. Each slide is then 

 warmed until the wax melts and is 

 dropped into the jar of xylene. When the 

 slides have been in the first jar of xylene 

 long enough for the wax to have been re- 

 moved, they are transferred to the second 

 jar of xylene for a minute and then run 

 down the series to the jar of distilled 

 water. If the slide, on removal from dis- 

 tilled ^^■ater, appears to be greasy, it must 

 be run up the series through the alcohols 

 again into xylene, and then down. If the 

 least trace either of wax or xylene remains 

 in the section, staining cannot be carried 

 out. The slides are transferred one at a 

 time to the jar of 5% silver nitrate, which 

 is then placed in the paraffin embedding 

 oven (presumably at a temperature of 

 about 60°C.) where they remain for ap- 



