The Microscope. 341 



Bergamot oil is in every respect the best to use in celloidin 

 technique. Origanum oil may be used, but its action is violent and 

 often causes the colors to fade. Good bergamot oil is clear grass- 

 green, with at most a slight yellow tinge (yellow oil is always bad), 

 does not smell of terpentine, and mixes with 90 per cent, alcohol 

 without turbidity or formation of water drops on the surface. The 

 little cloudiness produced by breathing on the latter, should at once 

 disappear. Aniline colors ought not to fade perceptibly in berga- 

 mot oil even after forty -eight hours ; while celloidin ought not to be 

 softened by it in the least ; on the contrary, sections that have been 

 softened by strong alcohol should acquire greater firmness in berga- 

 mot oil. 



Tracing paper must first be cut into strips about as broad as the 

 object- carrier, and at least three times as long as the cover-glass. 

 The shape of the latter is marked on one end of the strips. The 

 paper must be perfectly smooth, well oiled and transparent, and 

 unite some stiffness with flexibility. The strip should be held by its 

 free third, horizontally, in the oil, supported from beneath by the 

 middle and third fingers, and held from above by the thumb and 

 first finger, so that a slight longitudinal and upwardly directed con- 

 cavity can be given to it. Thus the immersed end of the paper, on 

 which the sections are to be arranged, can easily bear a slight weight 

 without bending. Now, while the left hand holds the strip of paper 

 over the surface of the oil, the right draws the sledge of the micro- 

 tome with the little finger, and also turns the micrometer screw. 

 Between the middle and third fingers of the same hand, a fine elas- 

 tic brush is held, supported by the ball of the thumb, and between 

 the first and middle fingers and the thumb a very sharp but strong 

 dissecting needle. The section is removed from the knife, where it 

 lies in plenty of 95 per cent, alcohol, with the brush, and put on the 

 oil; here it is followed with the strip of paper held beneath and 

 guided near the position where it should lie ; then drawn with the 

 needle out of the oil on to the paper. Ths sections are arranged in 

 cross rows, which are held from 2 to 3 mm. out of the oil to prevent 

 them from swimming away. The rest of the paper remains in the 

 oil and is only withdrawn as it is covered with sections. When the 

 desired number of sections has been brought into order on the paper, 

 the oil is drained off, and the paper is then turned so that the sec- 

 tions face downwards. In this position the strip is allowed to fall 

 slowly on the object-glass. Then it is flattened out with a dissecting 

 needle and dried with blotting-paper. Now the tracing-paper, 



