Microtomes : their- Choice and Use 237 



give two successive clicks when vernier numbers 3 and 3 

 are in apposition. 



Quite a number of object-holders and various apparatus 

 have been devised for the use of this microtome to meet 

 the requirements of various workers. The beginner should 

 start by procuring the Neapolitan object-holder with jaws, 

 and subsequently obtain the other patterns as he feels the 

 need of them. This microtome has no absolute faults ; it 

 will fulfil the various requirements of the zealous worker in 

 a very satisfactory manner. It will be well, however, to 

 point out inconveniences which are not enumerated in the 

 maker's price-list. When cutting hard material or when 

 working with a large paraffin block, the object-holder is apt 

 to jump on its tramway at the impact of the knife, but as 

 these conditions are not usual the objection may perhaps 

 be shelved. A more serious complaint is that, when the 

 micrometer screw has been turned to the extremity of its 

 travel, it has to be turned back again, and then the whole 

 micrometer screw apparatus has to be pushed up the 

 inclined plane until the point of the micrometer screw 

 again touches the polished agate of the object-carrier, 

 against which it works. It will be readily seen that this 

 readjustment requires very considerable delicacy in its 

 manipulation. This matter is the greatest fault of the 

 instrument ; if the readjustment is not done perfectly, the 

 resulj; will be the losing of a few sections, and probably 

 just the most important of the series. 



The uninitiated will ask, ' Why lose sections ?' The fact 

 is, paraffin sections usually curl considerably upon the 

 knife until a few have been cut. When starting a ribbon, 

 the first few are consequently, as a rule, worthless, and 

 the readjustment of the screw, unless very carefully done, 

 means the starting of a new ribbon. 



To unwind the micrometer screw, a piece of waxed thread 

 passed once round its extremity and pulled in the right 

 direction will accomplish the task in a couple of seconds. 



Becker's Spengel and other Microtomes. — A micro- 



