PARAFFIN IMBEDDING 495 



Paraffin imbedding is to be chosen when very thin sections or serial 

 sections are desired. Material imbedded in paraffin may be kept for 

 years without any apparent deterioration. 



Celloidin Imbedding. Thick celloidin is prepared by dissolving 30 

 gm. of Schering's granular celloidin in 300 .c.c. of a mixture of equal 

 parts of ether and absolute alcohol. It has a thick syrupy consistency, 

 and becomes constantly denser by evaporation of the solvent. It should 

 be kept in a tightly closed preserve jar. Thin celloidin is prepared by 

 mixing equal volumes of the thick celloidin and the absolute and ether 

 mixture. 



The hardened and dehydrated block of tissue, trimmed to the size 

 and shape desired, is transferred from absolute alcohol to a mixture of 

 equal parts of ether and absolute for 24 hours. From this it is transferred 

 to thin celloidin, in which it remains from 24 hours to a week or longer, 

 and then to thick celloidin for the same length of time. The success 

 of the process depends largely upon the thorough infiltration of the 

 tissue with the celloidin. The time required in the celloidin varies with 

 the penetrability of the tissue and the size of the piece. 



After remaining for a sufficient length of time in the thick celloidin, 

 the tissue is taken out with a mass of adherent celloidin and is pressed 

 gently against the roughened surface of a block of vulcanized fiber. 

 As soon as a film has formed upon the surface, the block and attached 

 specimen are dropped into 80 per cent, alcohol, in which the mass becomes 

 firm. It is ready for sectioning in about 6 hours. 



In case it is desired to secure sections through the entire thickness 

 of the specimen, the following method is recommended. A sufficient 

 quantity of thick celloidin is poured into a flat dish (or paper box) and 

 the specimen is put into it. The entire mass is hardened as before and 

 then a block of celloidin containing the specimen is cut out. This is 

 trimmed to leave only a thin rim around the specimen. The block is 

 placed for a few moments in the ether-absolute mixture, and then dipped 

 in thick celloidin and pressed against the surface of a fiber block, which 

 has also been dipped in the ether-absolute mixture and in thick celloidin. 

 The mass is allowed to harden somewhat, and then is placed in 80 per 

 cent, alcohol. 



The imbedded specimen is kept in 80 per cent, alcohol until wanted 

 for sectioning. Celloidin imbedding is recommended for large objects, 

 or for those from which very thin sections are unnecessary. 



Rf SUME" OF IMBEDDING METHODS. 



Assuming that the tissues have been fixed and carried into 80 per 

 cent, alcohol, the steps in imbedding are as follows: 



