474 PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS 



pump will keep the gum in proper condition for cutting. The 

 sections are easily cut, as in other microtomes of this class, by 

 alternate movements of the screw, Z, and strokes of the razor. 



The instrument may also be used for cutting tissue imbedded in 

 paraffin or other mass, the object to be cut being secured in position 

 either by being gently heated at its under surface and pressed on the 

 plate, F, to which it firmly adheres on cooling, or by a simple clamp- 

 ing arrangement, which can be substituted for the freezing-chamber. 

 When used in this way large numbers of sections may be cut in series 

 by attaching to the razor a light support to receive the sections as 

 they are cut. 



FIG. 401. Cathcart's freezing microtome. 



Another most serviceable and admirable, because inexpensive 

 and efficient, microtome, especially for freezing purposes, was 

 devised by Mr. Cathcart ; and it is now presented in a simplified 

 and improved condition. The instrument is illustrated in fig. 401. 



In this form the clamping arrangements are much more perfect 

 than in the old form ; the principal screw and its milled head are 

 larger and more convenient ; the freezing-plate . is circular, and is 

 provided with an arrangement for preventing the ether, with which 

 the freezing is effected, from reaching the upper side of the plate ; 

 and the instrument is now so modified that it can be used for ordinary 

 imbedding as well as freezing. 



