O. The Celloidin Method 



Infiltration 



The celloidin process is used for subjects that are tough, brittle, 

 or friable (crumbly) . Paraffin does not afford adequate support for 

 sectioning such materials. One example of a subject for which the 

 celloidin process must be used is a graft union (Fig. 13.9 a) , in which 

 the incompletely united members must be kept intact before and 

 after sectioning. Another illustration is the preparation of pathologi- 

 cal materials which may be in such disintegrated, fragile (ondition 

 that the sections would fall apart without the celloidin matrix. 

 Sectors from large trees having wood, cambium and bark tissues 

 cannot be kept intact withoiu embedding in celloidin (Fig. 13.9 b, r) . 

 Unembedded small twigs are difficult to hold and orient for longi- 

 tudinal sectioning without some matrix. A twig or sector from a tree 

 can be embedded in celloidin, blocked as shown in Fig. 8.2 D-F, and 

 sectioned accurately in any desired plane. A properly selected piece 

 of material may yield 100 sections, uniform in thickness, orientation, 

 and staining jjroperties. Permanent slides can thus be made by the 

 hundreds at low cost. In some laboratories the celloidin method is 

 neglected, or e\en scorned, but tlie above illustrations sh(n\' that the 

 process has its place in any well-eciuipped, versatile laboratory. 



The matrix for the celloidin process is a form of nitrocellulose, 

 know^n by several trade names — celloidin, collodion, Parlodion, and 

 some less common names. Ihis product is sold in the loi in of shreds 

 or chips, packed dry or in distilled water. The latter method retards 

 the development of a yellow color. Celloidin shoidd be dried thor- 

 oughly before being dissolved lor use. Ihe most (oninionh used 

 solvent consists of approximately ecjual volumes of ether and methyl 

 alcohol. These reagents nnist be of the best qualii\ and auliydrous. 

 Five stock solutions of celloidin are usually used. These solutions 

 contain, respectively, 2, 4, 6, 8, anil 10 g. of dried celk)idin per 100 

 cc. of solvent. Fhese solutions are designated for convenience as 2% 

 celloidin, etc. 



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