hARDWICKE'S SCIENCE-GOSSIF, 



taken in this, as in the previous case, not to permit 

 the balsam to overflow the edges of the cover glass ; 

 otherwise, the cover will become firmly cemented to 

 the slip on which it is temporarily placed, and the 

 future processes rendered impossible or difficult, as 

 the cover glass bearing the section will have to be 

 detached by heat or otherwise from the supporting 

 slip. I may add that none but a careless and slovenly 

 worker need fear the overflow of balsam spoken of. 

 The section itself ought to be completely covered with 

 balsam. 



4th. Lay the glass slip with the cover-glass upon 

 which the balsamed preparation lies exposed, either 

 in a special dust-proof box (an ordinary object cabinet 

 with trays will do), or under a glass shade, for a.bout 

 twelve hours. If left thus exposed for much less than 

 twelve hours, e.g. for two or three hours only, the 

 balsam will not be reduced to the right degree of 

 consistency through the evaporation of the solvent 

 (benzol in this case). If exposed for much over 

 twelve hours, e.g. for twenty hours, the evaporation 

 will have progressed too far, but this may be rectified 

 by the addition of another small drop, and the ex- 

 posure continued for an hour or two more. If 

 examined after about the twelfth hour under the 

 microscope, it will be observed that all air bubbles 

 have disappeared. 



5th. Gently warm a clean glass slip, place it upon 

 the mounting tile* so as to show its centre, upon 

 which a drop of benzoled balsam should be placed ; 

 now remove the cover glass with its supported 

 preparation from the slip upon which it lay exposed 

 (a pair of blunt-edged smooth-tipped forceps will be 

 found useful here), pass it quickly over, not into, the 

 flame of a spirit lamp or Bunsen burner, and apply 

 it slantingly, section downwards this time, to the 

 warmed slip with its central drop of balsam. Squeeze 

 out the superfluous balsam, and lay the now com- 

 pleted slide aside for a couple of hours. The squeezed 

 out balsam, if there is much of it, may now be 

 scraped off with a small knife and the rest of the 

 balsam cleared off with a rag dipped in methylated 

 spirit. If it so happens that the cover-glass has not 

 sufficiently set after being laid aside for a couple of 

 hours, if left for double that time, it may be handled 

 with impunity, and thoroughly cleansed. 



Of course, the section may be placed upon a clean 

 glass slip, balsamed, exposed, and then covered with 

 a cover-glass, to the under side of which a drop of 

 balsam has been applied ; but the above plan will be 

 found the most convenient in the mounting of a large 

 number of sections — cxferientia docei.\ 



If air-bubbles arise through the application of too 



* A mounting tile of white pottery-ware about 6X8 inches 

 in surface, with lines painted upon it, to indicate the centres of 

 slides, 3X1, and 3X1*, is a useful adjunct to the microscopist. 

 A piece of white cardboard similarly marked may be substituted 

 for such a tile. 



t I choose to curtail^ the proverb, " Experientia docet 

 stultos." 



much new balsam after exposure, they will invariably 

 disappear in the course of a few hours. If, however 

 as sometimes though rarely happens, air-bubbles get 

 entangled in very reticular tissues and wear an 

 obstinately persistent aspect, the cover-glass should 

 be removed at once, a fresh drop of balsam applied, 

 exposure for two or three hours repeated, or for such 

 time as it may take to dispel the atmospheric demons, 

 another small drop of fresh balsam applied, and the 

 preparation covered and cleaned in the manner 

 directed above. 



In the case of all thick tissues, such as sections of 

 decalcified bone, teeth, cartilage, the rhizomes and 

 leaf-stalks of ferns, &c., it will be found, that what 

 I shall term the exposure method, is sufficient to 

 harden the balsam to such an extent, that their 

 curling tendencies are subdued or altogether checked 

 by that process. But to make success doubly sure, 

 such refractory sections may be flattened during the 

 clearing process. As soon as they sink to the 

 bottom of the oil of cloves, they are to be removed 

 to a clean glass slip with their adhering pools of the 

 oil, covered with another similar slip and the two 

 held together with an elastic band or piece of string, 

 and laid aside for a few hours (four or five). On 

 removal, and during the exposure method which 

 follows, they may recurl, but their limit of elasticity 

 has been greatly diminished by the continued pressure, 

 and they will be found to be quite manageable. 



Whilst mounting very thick sections, in cells, or 

 otherwise, the benzoled balsam will evaporate during 

 the exposure process, and should be replenished at 

 the end of the twelfth hour, exposed for another three 

 hours, re-added to with a small drop of fresh balsam, 

 and covered. Vacuolar spaces cannot possibly appear 

 after these precautions. 



One of the most important things in balsam 

 mounting is the preparation of balsam of suitable 

 consistency. To secure a good result, some viscid 

 balsam should be placed to harden in a sand or water 

 bath. An old glue pot provided with a cover will do. 

 The hardening of the balsam must be conducted 

 gradually, to avoid burning the material. It should 

 be tested from time to time, by the removal of a 

 small quantity upon a rod. As soon a:s the material 

 removed hardens into an almost brittle mass upon 

 cooling, the still liquid hot balsam in its pot should 

 be taken off the flame, and an equivalent bulk of pure 

 benzol added to it. A little stirring with a glass rod 

 will accelerate the solution of the hot balsam, and it 

 should now be filtered through a cone of fine filter- 

 paper. The filtrate should be of the consistency of 

 thick syrup. If too thick, a little more benzol should 

 be added and the process continued in a warm place, 

 in an oven or in front of a fire, preferably the former. 

 If too mobile, exposure to the air under a bell glass 

 will reduce it to the right degree of viscosity in a few 

 hours ; refiitration in a warm place will effect the 

 same end in a few minutes. 



