40 THE AMKKICAN MONTHLY [Fel.ruaiy, 



imbrtKlinj; incthotls. Tlic follo\viii<j; are practically usclul : iiu- 

 Ix'ildin;; in i;;uin. in cclloitlin, ami in paratVin. 



ImhfdJiHj^' in iium, — This is simple and sluniUl be used for 

 ordinaiy. evcrv-day work. The inihcddinji^ substance is a solu- 

 tion ot'«jnni arabic. Make a thick nuicilaLje with watei- and add 

 a crystal ot* carbolic acid to preserve it. For iiul>etldin^^ the thick 

 solution is thiiuieil by water until entirely clear. 



Tissues fixed by the foregoinjj; reay;ents are to be thus prepared 

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

 larjje vessel of water to remain till thev sink to the bottotu, where 

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

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

 from osmic and picric acids anil the bichromates should also be 

 washed in this way The specimen is placed in a wide- 

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

 mucilaj^e is poined till the object is entirely covered. In from 24 

 to 4S hours the tissue will be saturatcil. A very thin solution of 

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

 thicken as the water evaporates. With l)ibulous paper remove 

 the layer of ijum from the surface, and place the sjiecimen in a 

 large cjuantitv 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. 



Imbciidinff in CcUoidin. — Collodion may be used, butcelloidin 

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

 Cut into small j)ieces 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 2.4 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 tor 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 ; tlierefore 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 

 quicklv than with alcohol. We thus 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. \ 



