164 J. SOLLAS. 



The tissue to be cut is transferred from water to the melted 

 jelly, and should remain in it till well permeated. 



It is then placed on the piston of a Rutherford's microtome ; 

 the " well " should not be filled : for adherence it is sufficient to 

 roughen the surface of the piston with a file. No more jelly 

 should be used than is sufficient to surround the specimen ; if 

 too much has been added, it may be removed when frozen by 

 careful paring. 



When well frozen, slices may be cut in the ordinary way ; 

 while frozen they should be quickly transferred to the glass 

 slide on which they are to be mounted. On touching the 

 glass, the slice of jelly almost immediately thaws and adheres 

 as a consistent fibre to the surface. When enough slices have 

 been placed on the slide, they should each be covered with a 

 drop of glycerine (the sooner this is added the better) ; a cover 

 glass is then superposed, zinc white or some similar cement is 

 run round it, and the preparation is complete. In process of 

 time the glycerine will permeate the gelatine and convert it 

 into glycerine jelly ; if this does not take place soon enough, 

 it may be hastened by placing in an oven kept at a temperature 

 of about 20° to 30° C. 



In this way a series of entire slices of great thinness may be 

 obtained from the most disconnected structures ; even when 

 they contain hard silicious spicules, as in the case of sponges. 



Diatoms may be cut without difficulty by this method ; I 

 have now beside me some slices of Pleurosigma, which 

 reveal the internal anatomy of these organisms in an admirable 

 fashion. It need not be added that the process efi'ects a con- 

 siderable saving in labour and time. 



