130 NATURALISTS' ASSISTANT. 



jelly is used, water will accomplish this. After being freed, 

 they may be kept in alcohol or mounted as desired. In 

 handling sections the greatest care should be exercised. A 

 very convenient instrument is a section lifter, consisting of 

 a thin sheet of metal attached at an angle to a handle. 

 This is passed tinder a section floating in the liquid which 

 is gently lifted and floated off in the desired place. 



In case it be desired to keep the sections in consecutive 

 order, each as cut must be transferred to its proper recepta- 

 cle and properly labelled. 



To aid in cutting sections mechanical appliances have 

 been invented. These are known as microtomes or section 

 cutters. Of these many forms have been in use, the best 

 and most common being those described below. 



The simplest form is the Sterling microtome (so called 

 from its inventor) . This consists of a tube in which moves 

 a plug, regulated by a screw with a large graduated head. 

 The other end of the tube bears a large brass or glass plate 

 over the surface of which the razor passes. 



The method of using is simple : the embedded material oc- 

 cupies the tube resting on the plug, a slight turn of the 

 screw moves the whole forward, a slice is taken off with the 

 razor, and the process is repeated. 



By knowing the number of threads to the inch of the 

 screw, and the fraction of a turn which it made in cutting 

 each section, the thickness is an easy matter to ascertain. 

 This section cutter (as in fact all others) produces sections 

 with parallel surfaces, a rather difficult thing to obtain by cut- 

 ting free hand. 



