ARRANGEMENTS FOE SECTION-CUTTING 497 



' The chloroform and the objects in it are gradually warmed up 

 to the melting-point of the paraffin employed, and during the 

 warming small pieces of paraffin are by degrees added to the 

 chloroform. So soon as it is seen that no more bubbles are given 

 off from the objects, the addition of paraffin may cease, for that is a 

 sign that the paraffin has entirely displaced the chloroform in the 

 objects. This displacement having been a gradual one, the risk of 

 shrinkage of the tissues is reduced to a minimum.' After this, 

 however, the w^hole must be kept warm on the water-bath, 'at the 

 temperature of the melting-point of the pure paraffin employed, 

 until all the chloroform has been driven off from it, as, if even a 

 trace of chloroform remain in the paraffin, it will render it soft after 

 cooling. As this is a very long process (it may take days for large 

 objects), it is frequently better to simply transfer the objects from 

 the paraffin solution to a bath of pure paraffin. 



3. Arranging for cutting. After the objects have been duly 

 saturated, they are arranged in a suitable position for cutting, and 

 the paraffin is caused to solidify as quickly as possible. It must not 

 be allovied to cool slowly, as slow cooling allows the paraffin to 

 crystallise, and gives a mass less homogeneous and of a consistency 

 less favourable for cutting than after rapid cooling. 



Very small objects may be taken out of the paraffin with a 

 needle or small spatula, and put to cool on a block of glass, then 

 imbedded in position for cutting on a cone of paraffin already 

 soldered to the object-carrier of the microtome, or to a cork or 

 cylinder of wood fitted into it. This is done as follows : 



; A piece of stout wire, or a mounted needle, is heated in the 

 name of a spirit-lamp, and with it a hole is melted in the end of the 

 cone of paraffin ; the specimen is pushed into the melted paraffin, 

 and placed in any desired position. In the use of the needle or wire 

 it should be noted that it is important to melt as little paraffin as 

 possible at one time, in order that that which is melted may cool 

 again as rapidly as possible. The advantages of the method lie in 

 the quickness and certainty with which it can be performed.' 



If the paraffin bath has been given in a watch-glass, float the 

 watch-glass with the paraffin and objects on to cold water. Do not 

 let it sink till all the paraffin has solidified. When cool, warm the 

 bottom slightly and cut out blocks containing the objects ; do thi& 

 with a slightly warmed scalpel. Then fix the blocks to the object- 

 carrier by means of a heated needle as above described. 



For many objects, other methods of arrangement are preferable. 

 These consist chiefly in causing the paraffin to solidify in a mould of 

 any desired shape. Paper trays are often used as moulds. 



To make paper trays, proceed as follows. Take a piece of stout 

 paper or thin cardboard, of the shape of the annexed figure (fig. 407) ; 

 thin (foreign) post-cards do very well indeed. Fold it along the 

 lines a a' and b V, then along c cf and d d' , taking care to fold 

 always the same way. Then make the folds A A', B B' , C C", D D', 

 still folding the same way. To do this you apply A c against A a, 

 ;m<l pinch out the line A A', and so on for the remaining angles. 

 This done, you have an imperfect tray with dogs' ears at the angles. 



K K 



