74 



THE AMERICAN MONTHLY 



[April, 



of 60° C, and leave it for the same 

 length of time. Indeed, if care be 

 taken that the temperature does not 

 materially exceed 60°, the specimen 

 may remain as long as convenient. 

 When the tissue is thoroughly saturat- 

 ed with melted paraffine, a small paper 

 box may be filled with melted paraffine 

 and the specimen placed in it to cool. 

 If properly imbedded, a cut surface 

 has a smooth and shining appear- 

 ance. No line of division must ap- 

 pear between the specimen and sur- 

 rounding paraffine. The whole mass 

 should cut, as nearly as possible, like 

 one homogeneous mass of paraffine. 



The subsequent handling of the 

 sections varies with their nature. 

 Moderately thick sections of firm tis- 

 sue may be placed in turpentine to 

 remove the paraffine and mounted as 

 usual in chloroform-balsam. Thin 

 specimens, or those which come to 

 pieces when the paraffine is removed, 

 like thin sections of liver, etc., may 

 be laid on the slide on which they 

 are to be mounted and the paraffine 

 washed out by benzine, carefully ap- 

 plied with a dropping-tube; allow the 

 benzine to evaporate, then lay on the 

 cover-glass and apply thin chloroform- 

 balsam at the edge of the cover. For 

 exceedingly delicate specimens, such 

 as embryos or osmic acid nerves, an- 

 other method may be used. Lay the 

 section on the slide, wet with absolute 

 alcohol and let the alcohol complete- 

 ly evaporate, leaving the specimen 

 attached to the slide; carefully heat 

 until the paraffine is softened, or 

 slightly melted. When cool, let a few 

 drops of benzine — best applied with 

 a brush — run over the section until 

 most of the paraffine is gone. When 

 dry, apply the cover-glass and put a 

 thin solution of Canada-balsam in 

 xylol to its edge. The xylol may be 

 used instead of benzine but it is more 

 expensive. 



This method is very convenient, 

 especially for histological laborato- 

 ries. The specimen once imbedded, 

 can be kept for years, and new sec- 

 tions cut as wanted. No change takes 



place in it nor can it dry up. It is 

 suited to all tissues. I have imbed- 

 ded all vertebrate soft tissues, chick 

 and trout-embryos, hydras, snails, an- 

 gle worms, clams, star-fishes, etc., with 

 equal success in every case. 



The ease with which the sections 

 can be made, fully compensates for 

 the time required to imbed. The 

 merest tyro, provided with a good 

 section-cutter, a brush to keep the 

 sections from rolling, and such a 

 specimen, must be a bungler indeed 

 if he cannot cut at least thirty even 

 sections from each millimetre of a 

 moderate-sized specimen such as the 

 oesophagus of a rabbit. With a little 

 practice he should be able to cut a 

 millimetre into one hundred sections 

 without losing more than two. The 

 writer has cut a frog's spinal cord so 

 imbedded into 926 sections -^ mm. 

 thick in one day, and mounted them 

 without losing any sections. No one 

 who practises with these specimens 

 will regard this as much of a feat. It 

 is simply a hard day's work. 



Specimens as large as the central 

 hemisphere of a rabbit can be stained 

 and imbedded whole. 



I append my notes on the spinal 

 cord of a frog, showing the times used 

 in the various processes: — 



Cord put into 3 per cent, nitric 

 acid, two hours. 



Seventy per cent, alcohol, six hours. 



Stained in haematoxylin, four hours. 



Seventy per cent, alcohol, over 

 night. 



Ninety-five per cent, alcohol, twen- 

 ty-four hours. 



Oil of cloves, twenty-four hours 

 (did not wish to imbed till next day); 

 then, 



Turpentine stir half-an-hour. 



Turpentine and paraffine, one hour. 



Paraffine, one hour. 



It should be remembered that these 

 cords imbed easily. 



One caution further — select paraf- 

 fine if possible, which is bluish-trans- 

 parent and which rings slightly when 

 struck. The white, opaque sort is by 

 no means as good. Any addition of 



