158 COLLODION SECTIONING. [CH. VII. 



three hours will suffice for objects two or three millimeters in thickness. 

 A stay of one or more days does no harm. The larger the object the 

 more time is needed. 



§ 256. Infiltration with Thick Collodion. — The thin collodion is 

 poured off and thick collodion (§ 304) added. For very small objects, 

 four or five hours will suffice to infiltrate, but for larger objects a longer 

 time is necessary. The tissue does not seem to be injured at all in the 

 thick collodion, and a stay in it during a da} r or even a week is more 

 certain to insure a perfect infiltration. 



§ 257. Imbedding. — The tissue may be imbedded in a paper box, 

 such as is used for paraffin imbedding, or in any of the other boxes de- 

 vised for paraffin. It is better, if paper is used, to put a very small 

 amount of oil on the paper to prevent the collodion from sticking to it. 

 Vaselin spread over lightly and then all removed, so far as possible, 

 with a cloth or with lens paper, gives the right surface. For small ob- 

 jects it is more convenient to imbed immediately on a holder that may 

 be clamped into the microtome. Cylinders or blocks of glass, vulcanite, 

 wood and cork have all been recommended and used. A cork of the 

 proper size is most convenient, and for many purposes answers well. 

 Some collodion is put on the end of the cork and a pin put near one edge. 

 The tissue is transferred from the thick collodion to the cork and leaned 

 against the pin. Drops of the thick collodion are then poured on the 

 tissue, and by moving the cork properly the thick, viscid mass may be 

 made to surround and envelop the tissue. Drops of collodion are added 

 at short intervals until the tissue is well surrounded, and then as soon 

 as a slight film hardens on the surface, the cork bearing the tissue is 

 inverted in a wide-mouth vial of considerably larger diameter than the 

 cork (Fig. 132). The vial should contain sufficient chloroform to float 

 the cork. The vial is then tightly corked. In imbedding somewhat 

 larger objects on the end of a cork or other holder, it is frequently ad- 

 vantageous to wind oiled paper around the holder or cork, tie it tightly 

 and have the projecting hollow cylinder sufficiently long to receive the 

 object. The tissue is then put into the cylinder and sufficient collodion 

 added to completely immerse it. As soon as a film has formed over the 

 exposed end, the cork may be inverted and immersed in chloroform, as 

 described above. 



§ 258. Hardening and Clarifying the Collodion. — -After a few 

 hours the collodion is hardened by the chloroform. If it acts long 

 enough the imbedding mass is rendered entirely transparent, if no water 

 is present. Whenever the collodion is hard, whether it is clear or not, 



