STAINS, ETC. 



1373 



EMBEDDING 



Nitric Acid. Twenty per cent, solution is a useful 

 medium for the maceration of muscle. After 24 hours' 

 treatment, the isolated fibers may generally be obtained 

 by shaking the tissue with water in a test-tube. Ni- 

 tric Acid and Glycerin. A mixture of glycerin 50 

 c.c, nitric acid 1 c.c. , and water 150 c.c. , is recom- 

 mended for isolating the elements of nerve tissue. 

 Nitric Acid and Potassium Chlorate, Kiihne's 

 od. Mix in a watch-glass one part of potassium 

 chlorate with four of nitric acid, and in this immerse 

 a fragment of muscle for half an hour, and then shake 

 it with water in a test-tube to separate the fibers. 

 Oxalic Acid. Maceration for several days in a 

 concentrated solution has been found useful in the 

 examination of nerve-endings. Potassium Perman- 

 ganate. See Fixing Fluids. Salt-solution. A 10 

 per cent, solution of sodium chlorid is a valuable mac- 

 erating agent for white fibrous and other tissue. 

 Schiefferdecker's Methyl Mixture. Methyl alcohol 

 5 c.c, glycerin 50 c.c, distilled water 100 c.c. Used 

 for dissociating the retina and other nerve-tissues. 

 Macerate the perfectly fresh tissues for several days. 

 Sulphuric Acid. Recommended by Max Schultze for 

 isolating the fibers of the crystalline lens. Macerate 

 for 24 hours in 30 c.c. of water containing 4 to 5 drops 

 of pure sulphuric acid, and then agitate. Very dilute 

 sulphuric acid is stated by Odenius to be the best 

 medium for the examination of nerve-endings in tac- 

 tile hairs. Hot sulphuric acid is used to dissociate 

 horny epidermic structures — hair, nails, horn. II. 

 Digestion Fluids. Bickfalvi's Fluid. One gram 

 of dried gastric mucosa is mixed with 20 c.c. of 0.5 

 per cent, hydrochloric acid, put into an incubator 3 to 4 

 hours, and then filtered. The tissue should not remain 

 in the solution for more than a half to one hour. 

 Brucke's Fluid. This consists of glycerinated extract 

 of pigs' stomach I volume, 0.2 per cent, hydrochloric 

 acid 3 volumes, and a few crystals of thymol. Kiihne's 

 Fluid. Trypsin is obtained by extracting the pancreas 

 of an ox with ether and alcohol, and evaporating to dry- 

 ness ; one part is then heated for 3 to 4 hours, at a 

 temperature of 40 C, with 5 to 10 parts of a O.I per 

 cent, solution of salicylic acid, the solution pressed 

 through linen, and filtered when cold. Kuskow's 

 Fluid. Pepsin one part, dissolved in 3 per cent, oxalic 

 acid, 200 parts. The solution should be freshly made, 

 and objects macerated in it 10 to 40 minutes at the 

 ordinary temperature. Schiefferdecker's Pancre- 

 atin Fluid. A saturated solution of pancreatin in 

 cold distilled water is made and filtered. Pieces of 

 epidermis are macerated in it for 3 to 4 hours, at about 

 the body-temperature. The forms of the prickle-cells 

 are clearly shown, and the nuclei are preserved. 



EMBEDDING. 



mbedding methods are divided into two classes, ac- 

 cording to the end which it is intended to accomplish : 

 I, simple embedding; 2, interstitial embedding, or 

 infiltration. Simple Embedding consists in sur- 

 rounding objects which are too small or too delicate 

 to be firmly held by the fingers or by instruments 

 with some plastic substance which gives them firm 

 support without injurious pressure, and thus allows 

 of the cutting of thin sections without distortion. 

 Among the materials used are: (i) Moist Paper. 

 Strips of printing paper softened in water are rolled 

 around the object, which, thus wrapped, is firmly 

 pressed into the microtome-cylinder. (2) Paraffin 

 Infiltration and Embedding. The initial step in this 



: process consists in the infiltration of the object with a 

 clearing agent ; that is, by some substance which is a 

 solvent of paraffin. It is then immersed in melted par- 



affin until it is thoroughly saturated. The paraffin 

 should be kept just at the melting-point and should be 

 renewed if the object is large. The duration of the 

 bath depends on the size of the object. When this 

 second step in the process is completed, embed in 

 paraffin, as in simple embedding. To prevent crys- 

 tallization of the paraffin, the embedded object should 

 be quickly cooled, which may be done by floating it 

 in the containing receptacle on cold water. When 

 chloroform is the clarifying agent, the subsequent 

 treatment differs from the foregoing, and is as fol- 

 lows : The object is saturated with absolute alcohol, 

 then brought into chloroform (containing a little 

 ether to prevent the object from floating), and then 

 penetrated ; the chloroform and the object are gradu- 

 ally warmed to the melting-point of the paraffin used, 

 small pieces of paraffin being added during the warm- 

 ing. When bubbles are no longer given off from the 

 object, the chloroform has been entirely displaced by 

 the paraffin, and the object is ready to embed {Gies- 

 brecht) . A little tray or box is made of paper, and some 

 melted paraffin is poured into it ; as soon as the mass 

 has cooled sufficiently to support the object this is 

 placed on its surface. More melted paraffin is poured 

 on until the object is enclosed. Boxes may be con- 

 structed by placing pieces of type-metal upon a 

 plate of glass which has been wetted with glycerin 

 and gently warmed. In such a box the paraffin may 

 be kept in a liquid state by warming over a spirit 

 lamp, thus allowing small objects to be placed in any 

 desired position by means of a heated needle under 

 a dissecting microscope. Small objects may be em- 

 bedded in the following manner: A hole is melted in 

 the end of a cylinder of paraffin by means of a piece 

 of wire which has been heated in the flame of a 

 spirit-lamp. The object is then pushed into the 

 melted paraffin and placed in the desired position. 

 The Watch-glass Method, which is unequaled for 

 small objects, is as follows : Melt paraffin in a 

 watch-glass, place the object in it, and allow it to 

 cool ; then cut out a block containing the object, 

 or the whole mass of paraffin may be turned out by 

 rapidly warming the bottom of the watch-glass. (3) 

 Pith. A cylinder of pith is halved longitudinally, a cav- 

 ity corresponding to the object to be embedded is made 

 by scooping out the inner face of either half-cylinder 

 and the object is placed between them. The cylinder 

 is then pushed into a microtome well and moistened 

 with alcohol, so that the pith may swell and firmly 

 enclose the object. Heidenhain s Modified Method. 

 Fix the object in a supersaturated solution of corrosive 

 sublimate made in a one-half percent, solution of com- 

 mon salt. After one-half hour's immersion, transfer to 

 95 per cent, alcohol, where it should remain 24 hours. 

 Clear in bergamot-oil and embed in paraffin. Sec- 

 tion, remove paraffin by xylol or benzine, and place 

 in 95 per cent, alcohol. Then treat 15 minutes with 

 pure tincture of iodin, to remove the excess of 

 corrosive sublimate, and place again in 95 per cent, 

 alcohol. The sections are now ready for staining. 

 Interstitial Embedding. Practically, this is a pro- 

 cess of hardening. The natural cavities of the 

 object are filled with the embedding mass, and each 

 separate anatomic element surrounded with the 

 supporting substance, thus securing firmness and at 

 the same time ensuring natural relations of all structu- 

 ral details. The materials mainly used are Paraffin, 

 for small sections, and Cello/din, or collodion, for large 

 sections. Embedding Masses. The most gener- 

 ally useful is pure paraffin, melting at 45 C. Soap 

 Masses are very penetrating, and have the advan- 

 tage of being transparent and of cutting better than 



