IMPROVED METHOD OF USING THE FREEZING MICROTOME. 163 



An Improvement in the Method of using the 

 Freezing Microtome. 



By 



J. Sollas, IVI.A., 



Professor of Geology in Trinity College, Dublin. 



The process of obtaining thin slices of soft structures by 

 means of embedding in paraffin has now been brought to a 

 state of almost ideal perfection ; on the other hand the method 

 of " freezing " still remains almost in its infancy. At present 

 it is only with great trouble that a continuous series of slices 

 can be obtained with it, and if these are cut from a loose dis- 

 connected tissue, they break up immediately on being intro- 

 duced into water to free them from the gum in which they are 

 always embedded. Moreover, the waste of time involved in 

 transferring from water to a glass slide is simply appalling. 



Yet the freezing process has special advantages of its own. 



In the case of many tissues it affords a clearer insight into 

 structure ; perfect staining is not so indispensable (provided, 

 as is usually the case, glycerine be used as a medium for 

 mounting) ; and when hard parts occur in a preparation along 

 with soft, both may be evenly cut through with equal ease. It 

 is not likely, therefore, to fall wholly out of use, particularly 

 for certain refined histological work, and improvements may 

 be confidently expected. 



The following may perhaps be regarded as a first step to 

 others. Instead of freezing in gum, as is usual, one uses 

 gelatine jelly. This is prepared and clarified in the ordinary 

 manner. It should set into a stiff mass when cold; how stiff 

 will best be learned by experience. 



