36 BOTANICAL MICROTECHNIQUE. 



sections which can be cut from it are relatively thick as? 

 compared with those which may be cut from paraffine. 



Objects to be imbedded in celloidin must first be thor- 

 oughly dehydrated, preferably in Schultze's apparatus (cL 

 16). They are placed in a mixture of equal parts of abso- 

 lute alcohol and sulphuric ether, and then, after a few hours, 

 in a solution of celloidin in the above mixture, which should 

 contain, according to Busse (I), one part by weight of cel- 

 loidin to 15 parts of the solvent. After it is thoroughly- 

 penetrated by this solution, which will require from a few 

 hours to a few days, according to its size and nature, the 

 object passes to a stronger solution containing one part of 

 celloidin in 1 1 parts of the solvent ; and finally, after well 

 penetrated by this, to a still stronger one with the propor- 

 tion of one to eight parts. After remaining for a suitable 

 time in the last solution, the object is ready for imbed- 

 ding. For this purpose, a paper strip may be wound 

 tightly about the end of a small block of suitable size and 

 material, preferably of bass-wood or of vulcanized fibre, 

 so as to form the sides of a box whose bottom is the 

 end of the block. This box is now filled with the thick- 

 est solution of celloidin, and in it the object is placed 

 and oriented carefully by means of needles wet with the 

 ether-alcohol mixture. As soon as the solvent has evap- 

 orated sufficiently to form a firm film over the surface of 

 the mass, the whole may be immersed in alcohol, where it 

 becomes quite hard in a few hours. Since very strong 

 alcohol dissolves celloidin, it cannot be used ; and statements 

 vary widely as to the best strength for this purpose. Busse 

 (II) has found, however, that 85$ alcohol gives the best 

 results, both as regards the transparency of the celloidin 

 and the thinness of the sections which may be cut from it. 



The paper is removed from about the celloidin mass, 

 after it has hardened, leaving it attached to the block. 

 The mass is now trimmed to present a rectangular upper 

 face, and the block clamped upon the microtome so that the 

 object may be cut in the desired plane. 



To cut successful sections from a celloidin block, it is 



