e 



40 THE AMERICAN MONTHLY [February, 



imbedding methods. The following are practically useful : im- 

 bedding in gum, in celloidin, and in paraffin. 



hnbedding in Gum. — This is simple and should be used for 

 ordinary, every-day work. The imbedding substance is a solu- 

 tion of gum arabic. Make a thick mucilage with water and add 

 a cr^'stal of carbolic acid to preserve it. For imbedding the thick 

 solution is thinned by water until entirely clear. 



Tissues fixed by the foregoing reagents are to be thus prepared 

 for imbedding : The pieces taken from alcohol are placed in a 

 large vessel of water to remain till they sink to the bottom, where 

 they should lie for about 30 minutes. This procedure expels the 

 alcohol, which would prevent the entrance of the gum. Pieces 

 from osmic and picric acids and the bichromates should also be 



washed in this way The specimen is placed in a wide 



mouthed vessel (a saucer is admirable for this), into which the 

 mucilage is poured till the object is entirely covered. In from 24 

 to 48 hours the tissue will be saturated. A very thin solution of 

 gum should be used, as it penetrates the tissues better, and will 

 thicken as the water evaporates. With bibulous paper remove 

 the layer of gum from the surface, and place the specimen in a 

 large quantity of strong alcohol for from 24 to 48 hours. It may 

 be suspended by a thread, but this is unnecessary if the amount of 

 alcohol is sufficient. 



hfibeddbig in Celloidin. — Collodion may be used, but celloidin 

 is preferable, and maybe procured in tablets of from 40-50 grms. 

 Cut into small pieces and place them in a mixture of equal parts 

 of absolute alcohol and of ether. Make two solutions — one very 

 thin, the other syrupy. 



The specimen, removed from 90" alcohol, is placed for 24 hours 



in absolute alcohol Transfer to absolute alcohol with an 



equal volume of ether. In a few hours, one day if the piece be 

 large, it is placed in the thin celloidin for 24 hours, then into the 

 celloidin syrup. It is difficult to indicate the hours needed for the 

 penetration of the syrup, as it varies with the nature of the tissue. 

 Two or three days are a medium time, but it is better to be too 

 long than not long enough. 



The saturated piece is placed in a little paper box filled with 

 the syrup, and the ether evaporated till a pellicle forms on the 

 surface. The evaporation should be slow ; therefore cover the box 

 with a bell-glass. The hardening is finished by plunging the box 

 into 82° alcohol. For small objects chloroform may replace the 

 alcohol. With it a consistent substance may be obtained more 

 quickly than with alcohol. We tluis obtain a transparent mass 

 from which we carve a block containing the object, and preserve 

 it in 82"^ alcohol or in chloroform till ready for sectioning. 

 [^To be continued. \ 



