AND HOW TO USE IT. 247 



clears perfectly in oil of cloves. The mass holds together all parts 

 of the section, and is therefore of much use for delicate structures. 



Freezing in Gelatine.* — Instead of freezing in gum, as is 

 usual, we use glycerine jelly. This is prepared and clarified in the 

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

 stiff will be best learned by experience. 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 Rutherford's 

 (or any other maker) microtome ; the " w^ell " should not be filled; 

 but for adherence it is sufficient to roughen the surface of the 

 portion with a file. Use no more jelly than is necessary to 

 surround the specimen ; if too much has been added, it may 

 be removed by carefully jDaring when well frozen. Slices may be 

 cut in the ordinary way, and should be quickly transferred to the 

 glass slide on which it is to be mounted. On touching the glass, 

 the slice of jelly almost immediately thaws, and adheres as a 

 consistent film to the surface. When enough slices have been 

 placed on the slide, cover each 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 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 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, siliceous spicule, as in 

 the case of sponges, diatoms, as Pleurosigma^ etc., they may be 

 cut without difficulty. 



Cutting Sections in Ribbons, t — The object of the process 

 is to enable the observer to cut a series of extremely thin sections 

 of any soft preparation, such as an embryo, and to mount the 

 sections in a series in the order of succession, retaining all the 

 parts of the specimen in their proper position. The specimen is 

 first properly prepared, and embedded in paraffin. The parafiin 



* Quart. J. Micro. Science. 

 t Am, M'onih. Journal of Micros, 



