ON STAINING FLUIDS, AND STAINING. 125 



against the same part or bit of the frozen tissue, and 

 raise or lower either end by screwing either of the 

 two screws nearest to us. All is now complete, and 

 we cut section after section by lowering the knife 

 edge for each fresh cut by giving the screw furthest 

 away from us a part of a revolution. 



To Fill an Ice Microtome. 



Get a piece, or pieces, of ice the size of two closed 

 fists, and the same bulk of either common table salt 

 or, even better, of bay salt. Powder both, and 

 thoroughly mix them. The ice is most readily 

 reduced to fine powder by being surrounded with 

 flannel and bruised with a broad-faced hammer, 

 or a carpenter's mallet. Fill in the mixed ice 

 and salt and press it well down, but take care that 

 the trough of the microtome is not so full that the 

 top touches the ice and salt. The top is to be placed 

 on the microtome and screwed fast. In winter the 

 machine, after being charged, is ready for freezing 

 in five minutes or so ; in summer it may be ten 

 minutes or more. Freezing proceeds, as we have 

 before said, for an hour or two. The waste pipe at 

 the bottom of the microtome is to be connected 

 by caoutchouc tubing, with a basin to receive the 

 melted ice. 



The disadvantage of Williams' microtome is, that, 

 like all ice microtomes, it is disagreeable to charge 

 even when ice is plentiful, and cutting must take 

 place at the time the machine is charged ; that is to 

 say, if the operator is called away, as in medical 

 practice often happens, his ice charge melts and 

 has to be renewed. 



