132 naturalists' assistant. 



It consists of a heavy oblong base about four by ten 

 inches and about a quarter of an inch in thickness. Arising 

 from this base is an upright plate ; on either side of these are 

 "ways," those on one side being horizontal and on the other 

 slightly inclined. On the horizontal ones a carrier travels 

 holding the knife, while on the other a second carrier is 

 borne, moved by a screw. This second carrier holds the 

 embedded specimen. Its method of operation is as fol- 

 lows : the embedded material is placed in the carrier which 

 is moved forward and upward until it is high enough to cut. 

 Then the knife is slowly but steadily drawn across the end of 

 the embedded object. The knife is then returned, the screw 

 turned the fraction of a revolution, and then another sec- 

 tion cut. Of course the knife is to be constantly wet with 

 alcohol. A valuable addition to this instrument may be made 

 by having the object carrier mounted on a universal joint, thus 

 permitting any desired inclination. Some sections of this 

 model are made of wood and are good for nothing. 



Dr. Seller's microtome is well shown in the figure and 

 needs no further description. It possesses this advantage 

 over all others, that the knife has a drawing motion. 



Freezing microtomes are sometimes employed. These 

 are generally of the Sterling pattern and have an attachment 

 by which a considerable degree of cold may be obtained 

 either by ice and salt or by ether spray. 



