The Celloidin Method 81 



A low-viscosity nitrocellulose has been recommended for rapid 

 infiltration of firm materials (Davenport and Swank 1934; Koneff and 

 Lyons 1937). Ihis inexpensive celloidin forms a firm matrix, and 

 its solutions in ether-alcohol tolerate 6% water, thus minimizing the 

 extreme brittleness produced in woody materials by total dehydration. 

 The above references give complete details of procedure. 



Hardening and Blocking 



In the celloidin process the solvent is not eliminated completely 

 during infiltration. The thickened celloidin solution is hardened 

 by immersion in chloroform. Remove an infiltrated piece of material 

 and a mass of enveloping celloidin and immerse in chloroform. The 

 celloidin loses its stickiness at once and soon becomes hardened 

 throughout. It is best to leave the material in chloroform for 12 hr. 

 to harden the celloidin in the innermost cells of the material. Trans- 

 fer the hardened material into a mixture of approximately equal 

 volumes of db'^i ethyl alcohol and glycerin, in which the material 

 may be stored indefinitely. 



Large pieces of embedded wood may be removed from the glycerin- 

 alcohol, clamped directly into the microtome, and sectioned. Subjects 

 having easily separable soft tissues are often damaged by compression 

 in the clamp. Such materials are sectioned best by mounting them 

 on blocks of wood or plastic. The mounting block may then be 

 clamped rigidly into the microtome clamp without damaging the 

 tissues. A twig or other long slender object should be mounted into 

 a plastic tube or a wood block having a hole of suitable size drilled 

 lengthwise through the mounting block (Fig. 8.2 A-C) . Prepare 

 mounting blocks by drying them thoroughly in a 110°C. oven, soak 

 in anhydrous methyl alcohol, then store in waste 4% celloidin until 

 needed. When the material being infiltrated is put into 8'^( celloidin, 

 drop a prepared mounting block into the specimen bottle and continue 

 the infiltration. 



To mount twigs for cutting transverse sections, remove the desired 

 twig and a stutable drilled mounting block from the thickened 

 celloidin. and push the twdg into the hole, leaving 6 to 10 mm. of 

 the twig protruding. Fill any space remaining around the twig by 

 pushing slivers of matchstick into the hole from below. AVrap a 

 generous mass of thick celloidin around the twig and mounting 

 block, and harden in chloroform (Fig. 8.2 C) . For longitudinal 

 sections of a twig, lay the infiltrated twig on a large, undrilled block, 

 wrap well with additional thick celloidin, and harden in chloroform. 



