30 the method op section-cutting with improvements, 



Cutting. 



The paraffin Ijlock should cool down slowly, and be made as 

 cold as possible before cutting. The colder the paraffin the 

 harder, and the harder the better, 



Caldwell recommended a very ingenous method of cutting 

 sections which has been adopted in sevei-al places, but which is 

 in pi-actice by no means so beautiful as in theory. 



He encloses the hard paraffin with a thin coating of soft paraffin, 

 and in cutting, the one section sticks to the opposite margin of the 

 other. If cutting is continued a " ribbon " of sections is produced 

 which can be caught up by a moving bit of tape, and poi^tions of 

 which can be cut out showing continuous series of sections. 



The Pai-affin block can be either cut by the hand or placed in a 

 section-cutting apparatus termed a Microtome, and cut either by 

 hand or automatically. 



Cutting with the hand has been nearly universally abandoned 

 (Leuckart), and the Microtomes are used for the purpose. The 

 principal always is, that the knife moves backwards and forwards 

 whilst the paraffin block is slowly raised. Or the knife is steady 

 and the paraffin block lises and moves backwards and forwai'ds 

 at the same time. (Caldwell.) In the simpler instruments, one 

 moves the holder of the knife backwards and forwards in a metal 

 groove with the right hand, and i-aises the specimen to be cut, 

 with the left either by pushing it up along an inclined groove. 

 (Leiser), or by turning a screw (the common form.) 



Automatic Mici'otomes are made by the Cambridge Mechanics' 

 Institution, which can be worked by water power or by ti-eading, 

 and the model has been copied by many with diverse alterations. 

 These automatic instruments yield very excellent results as long 

 as they are in order, but being so complicated they are apt to get 

 out of order. These are all adapted for the ribbon method and 

 sections of any desired thickness that is to the limit at which the 

 sharpest razor at a certain angle will cut can be made in 

 continuous series of specimens, measuring two inches across. 



To all these instruments the same remarks apply, and every- 

 where the same difficulties are encountered. 



