274 TECHNIQUE 



From ether-alcohol mixture to celloidin No. 3 (thin), for three 



to four days. 

 From celloidin No. 3 to No. 2 celloidin (medium), for four to 



six days. 

 From celloidin No. 2 to No. 1 celloidin (thick), for fi^'e to eight 

 days. 



At the end of this time the tissue should be completely saturated 

 with celloidin. We can proceed from this point in two ways: 



Fashion a little paper receptacle and fill it with celloidin No. 1. 

 Add but a few drops at first and wait a moment until they thicken, 

 add a few more drops, and then fill the receptacle. The tissue piece 

 is then placed in the box and arranged properly, with a view to 

 plane of sections to be cut later. The surface of the celloidin 

 rapidly forms a film when exposed to the air. Evaporation of the 

 solvent (ether-alcohol), with consequent hardening, should be per- 

 mitted to proceed slowly until the celloidin mass is like a heavy 

 gum in consistency. The paper receptacle is now carefully trans- 

 ferred to a covered glass dish containing chloroform, where hardening 

 is completed. The chloroform causes the celloidin to harden suffi- 

 ciently in one to two hours, when the paper box and excess celloidin 

 can be cut away and the embedded block can be placed in a bottle of 

 one-half 95 per cent alcohol + one-half glycerin until ready for 

 cutting. 



The other method both embeds and mounts the tissue preparatory 

 to sectioning. Vulcanized fiber blocks formed to fit the clamp of 

 the microtome should be used. Do not use wood blocks. The 

 solvent in the celloidin mixture extracts oils from wood and these 

 discolor the preparation. A strip of stiff paper is fastened about 

 one end of the fiber block so that a receptacle is formed at this end. 

 Celloidin No. 1 is added, drop by drop, to this receptacle, covering 

 the bottom of it with a relatively solid coat which is allowed to 

 thicken before filling the receptacle with celloidin from the specimen 

 bottle. The tissue is transferred also and oriented in the celloidin 

 which covers it on all sides. The celloidin is then permitted to 

 harden somewhat in the air, as in the first case, and then the block 

 Avith the celloidin-filled receptacle is transferred to a covered dish 

 of chloroform. After hardening in chloroform the block is stored, 

 as in the first procedure. 



If the first method was used it is necessary to fasten the celloidin 

 block to a fiber block before cutting sections. To do this thick 

 celloidin (No. 1) is poured over one end of the fiber block and over 



