IMBEDDING METHODS. 95 



seems to be a very simple one. Celloidin does not afford by 

 a long way the thinnest sections that are obtainable with 

 small objects. For such objects it is, therefore, not equal to 

 the demands made by modern minute anatomy, and paraffin 

 must be taken. On the other hand, paraffin (as at present 

 employed) will only cut very thin sections with fairly small 

 objects ; with objects of much over half an inch in diameter 

 you cannot get with paraffin thinner sections than you can 

 with celloidin ; and if you try to cut in paraffin objects of 

 still greater size, say an inch and upwards, it will frequently 

 happen that you will not get perfect sections at all, blocks 

 of paraffin of this size having a tendency to split under the 

 impact of the knife ; so that for very large objects celloidin 

 generally gives better results, in this respect, besides pre- 

 senting certain advantages for the manipulation and staining 

 of the sections. 



This defect is, however, much reduced by the employ- 

 ment of a softer paraffin than is usual. In this way STEASSER 

 (Zeit. f. iviss. Mik., ix, 1892, p. 7) has obtained series of 

 frontal sections 30 /u thick through the entire human brain, 

 in paraffin blocks measuring 10 x 15 cm. 



I have not been able to satisfy myself that the preserva- 

 tion of the tissues is better in celloidin sections than in 

 paraffin sections ; so that convenience apart the case 

 remains as above stated, paraffin for small sections, cel- 

 loidin for large ones. 



To these may be added aqueous masses, such as gum or 

 gelatin, for very special cases. 



