SMITHjS SECTION INSTRUMENT. 



203 



may in a great measure be prevented by having the 

 branches wide at the "base where they are riveted. The 

 points can be sharpened on a hone, and a magnifier em- 

 ployed to examine if they fit closely together. 



Section-cutting Instruments. — There are a numerous class 

 of substances much too hard to admit of beincr cu t either 

 by scissors or a Valentin's knife, more especially if we re- 

 quire very thin and perfect sections. As most important 

 information is to be gained respecting the structure of 

 various substances, such as stems and roots of plants, 

 horns, hoofs, cartilages, and other firm parts of animals, 

 by cutting very thin sections for mounting as transparent 

 objects, it would be quite impossible for the microscopist 

 to get on without a section-cutting instrument. Among 

 the many mechanical contrivances which have been de- 

 vised for the purpose, the ingenious little machine in- 

 vented by Mr. James Smith 1 will be found to do its work 

 with neatness and precision. 



Vertical or top view. 



Side view. 



Fig. 131. — Smith's Section Instrument. 



Smith's Section Instrument (fig. 131) consists of an outer 

 tube a, a, the upper part of which screws into the lower, 

 and has at the top a flat circular plate e, e, which 

 forms the cutting-table. . Firmly fixed to the lower part 

 of the tube a, and extending throughout its whole length, 

 is the inner tube b, b, which forms, with the moveable 

 bar d, a holding for the specimen to be cut, while, at the 

 same time, it supports the upper part of the tube a, a, and 

 gives it greater firmness in screwing up and down. The 



(1) " On a Section Instrument, by James Smith." (Micros. Soc Trans. 

 voL viii. page 1, I860.) 



