150 



THE ART OF MAKING MICROSCOPE SLIDES 



T.S. Lily bud 



described (Chapter 12) and should be em- 

 ployed in the case of the lily bud. Remem- 

 ber that almost nothing can prevent the 

 production of a perfect celloidin section 

 except imperfect dehydration of the speci- 

 men. One is only safe when the specimen 

 has remained in a large vessel of absolute 

 alcohol, containing copper sulfate at the 

 bottom, for a period of 24 hours, at the 

 end of which time not the slightest trace 

 of color shall have been accjuired by the 

 copper sulfate. 



A 16% solution of celloidin is then di- 

 luted to a strength of 2%. If the lily bud 

 contains very large cavities — that is, if it 

 was taken quite late in its development — 

 it may be necessary, in order to avoid 

 diffusion currents and some consecjuent 

 bending of the internal structures, to start 

 with a solution as weak as M% celloidin 

 rather than with the conventional 2%. It 

 is best to fix and dehydrate several buds at 

 one time and to take the first of these up 

 through the conventional process. If this 

 fails a slower method must be used. The 

 bud is then passed to a mixture of equal 

 parts of absolute alcohol and anhydrous 

 ether until diffusion currents are no longer 

 apparent. If only 20 or 30 milliliters of the 

 fluid are used for a specimen of this size, it 

 should be changed after about 3 hours and 

 then left overnight in a fresh solution. 

 There is a risk, if an object of this size is 

 picked from alcohol-ether mixture and 

 placed in another fluid, that the rapid 

 evaporation will leave air bubbles; there- 

 fore, it is best to place it in a vessel with 

 just enough alcohol-ether mixture to cover 

 it and then to fill this vessel with 2% 

 celloidin. The container is then rocked 

 gently backward and forward to mix the 

 celloidin, and the specimen is left for about 

 24 hours. This weak celloidin is now 

 poured off, leaving enough of it to cover 

 the object, and 4% celloidin is poured in. 

 The 4:% celloidin should be left for three 

 or four days and then replaced in the same 

 manner by 8% celloidin, in which the 

 specimen should be left for at least a week. 

 Eight per cent celloidin is sufficiently vis- 

 cous to inhibit air bubbles when the speci- 

 men is transferred, and it should now be 

 lifted from this thickish celloidin and put 

 into the 16% solution. All these operations 



should have been conducted in glass-stop- 

 pered bottles kept in a desiccator. The 

 period of time in 16% celloidin is not crit- 

 ical but two or three weeks would be a safe 

 period. The whole process is so long drawn 

 out, that an extra week or two makes little 

 difference; any endeavor to save even a 

 few days in the final impregnation may 

 undo all the previous work. 



Now take a wooden block about 1" X 

 1" X 2" and tie onto it a paper collar 

 (Fig. 80) at least an inch taller than the 

 bud. This is naturally a somewhat cum- 

 bersome arrangement; it will probably be 

 best to use an ordinary 5" X 3" indexing 

 card, rather than a piece of paper, in order 

 to get the necessary stiffness. A large box 

 of this kind will inevitably leak so that the 

 overlapped edges should be held together 

 with gum arable, permitted to harden, and 

 then dried in a desiccator. After this block, 

 with its paper walls rising from it, has 

 been thoroughlj^ dried in a desiccator, the 

 paper, and about half of the wooden block, 

 is dipped in 8% celloidin and placed back 

 in the desiccator. This procedure not only 

 holds the paper more firmly in position 

 but also provides an additional assurance 

 against leakage. When this initial coat of 

 celloidin has hardened, about '^2 inch of 

 16% celloidin is poured into the bottom 

 of the box, which is then returned to the 

 desiccator and examined at intervals until 

 the celloidin is found to have hardened 

 sufficiently to bear the weight of the bud. 

 The box is then filled with 16% celloidin 

 and the bud is inserted. It does not matter 

 in the least if the celloidin flows up over 

 the side, but it will be very unfortunate if 

 not enough of it is used. The writer finds 

 that the best method of holding a large 

 object like this in place in the box is to 

 take a couple of entomological pins and 

 drive them clear through the box and the 

 specimen, in areas from which sections are 

 not required. Using a long needle it is then 

 possible to reach down and adjust both 

 the bottom and the top of the long bud so 

 that it lies essentially in the center of the 

 box, held in place by the entomological 

 pins driven through it. Fine pins of this 

 nature do not make a sufficiently large 

 hole to permit any leakage of celloidin. If 

 the box is now not full of celloidin, it is 



