662 Caldwell's automatic microtome. 



The lock nuts (figs. 1 and 2, s) should be screwed up suffi- 

 ciently tight to barely prevent the carriage from falling by its 

 own weighty so that when the milled head (fig. 2, c) is screwed 

 down a slight pressure with the finger is necessary to make the 

 carriage fall. 



To arrange the machine for cutting different sized blocks of 

 material, it is" only necessary to raise or lower the arm (figs. 1 

 and 4,y). When this arm is in a vertical position, the machine 

 is arranged for its maximum traverse. When turned to the 

 right and placed horizontally, it is at its minimum traverse. 

 The cord, however, must always be in the groove of the 

 wheel k. 



It is important to keep the strings which give motion to the 

 endless band in proper position. The string (fig. 1, /) should 

 go from the end of the wire m round the groove n in the pulley 

 and thence to the elastic band o. The elastic band o should 

 be stretched and placed over the hook attached to the arm p, 

 care being taken that the shorter end of the arm p is upper- 

 most. The string g should be tied to the stud upon which the 

 arm p is supported, going thence round the groove ?• of the 

 pulley, and back again to the hook at the longer and lower 

 end of the arm p, to which it should be tied. 



Embedding Material.— The ribbon method of cutting 

 sections depends very much upon the temperature of the room 

 in which the operation is performed, since any given sample of 

 paraffin will only cut within a small range of temperature. To 

 meet this difficulty suitable embedding material has been pro- 

 duced, so that sections may be satisfactorily cut within a very 

 considerable range of temperature, obviating the necessity of 

 exactly adjusting the temperature of the room to the specimen 

 of paraffin in use, or as an alternative, of providing a number 

 of specimens of paraffin with diff'erent melting points. 



Method of Preparing the Slide. — Make by the aid of 

 heat a viscid solution of white shellac in light-coloured creosote. 

 Spread a smooth, thin, and even layer of this solution on a 

 clean dry slide, with a camel hair brush or with the little 

 finger. Arrange the ribbon containing the sections on this 



