24 THE METHOD OF SECTION-CUTTING WITH IMPROVEMENTS, 



and enclosed it between bits of fresh liver. The whole was then 

 placed in strong spirits, where the liver, together with the gum- 

 glycerine, got very hard, and enclosed the specimen which was 

 afterwards cut by hand. This method is an old one, and has 

 often been used befoi'e for less tender animals than those, to 

 which the brothers Hertwig have applied it, namely, the small 

 jellyfish. 



Sollas (Sponge Fauna of Norway, Annals and Magazine of 

 Natural History, 1879) recommends the freezing Microtome. The 

 specimen is placed in glycerine-gelatine and hardened, not by the 

 influence of spii-its of wine but by cold, which is produced by a 

 small refrigerating apparatus. The specimens treated in this way 

 are cut by a machine or Microtome. 



Both the sections cut in liver and with the freezing Microtome 

 cannot be placed in Canada balsam but must be kept in glycerine 

 or gelatine and are consequently liable to attain too great a trans- 

 parency in course of time and also to get dim in consequence of the 

 growth of Bacteria under the cover glass. 



The method which is recognised as the very best by most 

 microscopists is the one which I have been using and improving 

 for several yeai-s, .and a description of which follows. 



The Specimen. 

 It is of great importance that as small a piece as possible should 

 be cut out of the organ, that all unnecessary parts should be cut 

 away and the whole thing cut into such a shape that it will after- 

 wards be easy to find out what position the specimen had in the 

 organ from which it has been taken. 



Hardening. 



To small and tender organs osmic acid can be recommended as 

 yielding better results than any other re-agent known. The 

 specimen is placed in a solution varying in strength from 0-5 — 2% 

 and left there for a short time. Both time and strength depend on 

 the nature of the organ which is to be cut. 



Corrosive sublimate, a concentrated solution to be used, which 

 may be made stronger by warming. The specimen, if tender, 



