PREPABATION AND MOUNTING 



nitre is tdus polished on both its surfaces, which 

 be brought as near as possible to parallelism." 



Some sections of the naturally formed crystals also show 

 the " rings " very well, as Iceland spar, which gives a 

 single ring and cross; but the difficulty of cutting and 

 polishing them is almost too great for the amateur, and 

 must be left to the lapidary. This curious phenomenon, 

 however, may be*seen by using a plate of ice uninterruptedly 

 formed of about one inch in thickness. 



Before concluding these remarks on sections, I must men- 

 tion a few difficulties which may be met with, and their 

 remedies. The foremost of these is the softness of some 

 objects, which have not resistance enough in themselves to 

 bear cutting even with the sharpest instruments. This may 

 often be removed by soaking in a solution of gum, and then 

 drying, which will render the substance firm enough to be 

 cut, when the sections must be steeped in water, and the 

 gum thus removed. Small seeds, &c., may be placed in 

 wax when warmed, and will be held firmly enough when it 

 is again cold to allow of them being cut into sections.* 

 And, lastly, where a substitute for a microscopist's hand- 

 vice is required, a cork which fits any tube large enough 

 may be taken and split, the object being then placed between 

 the two parts, and the cork thrust into the tube, a sufficient 

 degree of firmness will be obtained to resist any necessary 

 cutting. 



* Mr. T. K. Parker informs me that he uses paraffine as an " ob- 

 ject-support " when sections are required, as follows : " The mixture 

 I use for embedding objects consists of solid paraffine (ordinary paraf- 

 fine candles will do very well) melted down and mixed with a little 

 paraffine oil, without which the paraffine is too hard to be easily cut. 

 The mixture when cold is cut into suitable pieces, a hole is scooped 

 out in the centre, the object to be cut placed in it, and a little of the 

 melted mixture poured round it. The sections are cut with an ordi- 

 nary razor, which, as well as the object, must be continually wetted 

 with spirit. This method is useful for all objects which are either too 

 Email for the hand or too soft or brittle to be cut in the ordinary way. 

 It is especially useful for histological specimens, leaves, embryos, 

 Ac." 



