1899] MICROSCOPICAL JOtJilNAL, 2ll 



a thin condition, it is not so in its more viscid form, and 

 it is necessary very frequently to cut tlie materifj,! small, 

 and open up closed cavities wherever possible. Still, for 

 insect preparations, cytological, and embryological work 

 generally, it is by many good workers preferred to para- 

 ffin, provided time is no object, as the process of infiltra- 

 tion is much slower. 



Celloidin is prepared from pyroxylin, and is usually 

 sold in the form of hard, horny, transparent shavings or 

 chips, but when obtained from Grrubler's Laboratory is in 

 flat, milky-white, semi-translucent cakes, of the consist- 

 ency of cheese. In this condition it smells strongly of 

 ether, and, on exposure to the air, shrinks and dries to a 

 horny consistency. It is perfectly soluble in ether or ab- 

 solute alcohol, and in some essential oils, but not in the 

 slightest degree in rectified spirits. The objects to be 

 cut are prepared by infiltration, and for this purpose the 

 celloidin must be dissolved in equal parts of absolute al- 

 cohol and ether, forming, practically speaking, a collo- 

 dion. It should be of at least two consistencies — the one 

 quite thin and watery, the other thick and syrupy. Noth- 

 ing having a vestige of aqueous matter must come into 

 contact with the solution. 



Method of Preparation of the Object. — Cut the fresh 

 tissue into pieces corresponding with the required size of 

 the sections, and after fixation thoroughly dehydrate in 

 absolute alcohol. This must be as carefully done as if 

 paraffin were to be used. The thorough expulsion of all 

 aqueous matter must be complete. The object may then 

 require passing through a bath of equal parts of ether 

 and absolute alcohol,if of a particularly obstinate nature; 

 but this will not be necessary with the average run of 

 material. And I may as well say here that the material 

 may be stained previously or not : but it is much prefer- 

 able to do the staining after cutting. The reason is not 

 far to seek. It is then easy to stain the object success- 



