METHOD OF MAKING PAPER BOXES 721 



and are so useful in confirming sections, that they are well worth the 

 trouble involved. 



If it is not convenient to carry out the whole operation at one time, 

 the preparation may be taken rapidly through the intervening alcohols 

 to seventy per cent, and allowed to remain there till it can be completed. 

 Staining, and sometimes decolorization, may be allowed to go on 

 overnight. 



Sections may be cut in either paraffin or celloidin, or by the combined 

 method. The former is applicable to soft tissues isolated from the 



chitinous parts, and the latter to whole parts of flies 



.. 11-1- i i i 1 1 . , Section cutting 



The ordinary celloidin method, though it has its 



advantages, has the very great disadvantage that serial sections cannot be 

 cut without a great deal of trouble. 



In cutting ordinary paraffin sections of isolated portions of tissue, 

 difficulties are chiefly met with on account of the small size of the part 

 and of the close association of the air-containing tracheae with the 

 tissue. The former difficulty is best got over by staining with eosin 

 previous to clearing ; a minute drop of watery eosin added to the first 

 change of absolute alcohol will make the part pink enough to be seen 

 when in the clearing agent and in the paraffin block. Tracheae should be 

 dissected off as far as possible before fixation, and the part should 

 always be examined carefully with a lens while in the paraffin bath to 

 ascertain if there are any bubbles of air still adhering to the tracheae. If 

 they are present they can usually be detached with a hot needle. 



Paper boxes* are the most satisfactory moulds for the paraffin blocks, as 

 they permit of much more manipulation than anything else. Watch 

 glasses (not the solid kind) are sometimes used, but they are not usually 

 deep enough to get a homogeneous block. They should be smeared with 



* Paper boxes for embedding, as shown in the text-figure, are made as follows. Take a 

 piece of paper preferably India paper about twice as long as broad, and make two folds in 

 the long direction, thus reducing the diameter to one-third ; double down each end of the 

 folded paper in two square folds, pressing them flat with the finger nail or a paper knife. 

 Now open out the paper flat. It will be seen that there are six squares at each end, in 

 transverse rows of three, and three oblong areas, which are to form the sides and bottom of 

 the box, in the middle. Bend up the squared ends till they are perpendicular to the bottom, 

 and make a diagonal crease in each of the corner squares, so that the side and end walls of 

 the box come in contact with one another. The squares with diagonal folds now form 

 triangular flaps on the outside of the box, and should be folded back so as to overlap one 

 another, as shown at the left side of the figure. The outer sets of squares, which are now 

 superimposed on one another, form flaps which serve as handles, and also provide a con- 

 venient place on which to note the details of the contents of the block. If several specimens 

 are to be embedded in the same block the paper from which the box is to be made should 

 be longer in proportion. 



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