17S COLLODION SECTIONING [CH.IV/ 



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

 exposed end, the cork ma}' be inverted and immersed in chloroform as described 

 above. For the use of "deck plugs" see § 274. 



\ 2J2- Hardening and Clarifying the Collodion. — After a few hours the 

 collodion is hardened by the chloroform. If it acts long enough, and if no water 

 is present, the imbedding mass is rendered entirely transparent. Whenever the 

 collodion is hard, whether it is clear or not, the chloroform is poured off and the 

 castor-xylene* darifier (''/. 317) added. In a few hours the imbedded mass will be- 

 come as transparent as glass and the tissue will seem to have nothing around it. 

 The tissue may remain for years in the castor-xylene. Sometimes the collodion 

 remains white and opaque for a considerable time. So far as the writer has been 

 able to judge, this is due to moisture. If one breathes on the mass too much while 

 imbedding, or if it is very damp in the room, opacity may result. Sometimes, in 

 objects of considerable size, this may remain for a week. This is the exception, 

 however, and if the mass seems sufficiently hard and tough, the cutting may pro- 

 ceed even if the clarification is incomplete, f 



In case the imbedding mass will not clarify after a few days the imbedded 

 object may be placed in 95",, alcohol for a day for dehydration, and then passed 

 through chloroform and into the clarifier. There is usually no trouble in getting 

 the mass perfectly clear in this way. 



If one is in a great hurry, the collodion may be hardened in 10 or 15 minutes 

 by heating the bottle containing the chloroform in a water bath. The imbedding 

 block of hardened collodion may then be transferred to the castor-xylene clarifier 

 and kept warm. It will soon clear the collodion. One can then cut the sections. 



\ 274. Cutting the Sections. — For cutting the sections the collodion block is 

 usually fastened to some form of holder. For small objects cork is fairly good. 

 Blocks of glass, vitrified fiber, etc., have been used. If one uses wood the "deck 

 plugs" of the shipwright are satisfactory. They are about the right length when 

 one plug is made into two holders by sawing in two (Ewing & Ferguson). To 

 fasten the collodion block to any form of holder, remove it from the castor-xylene, 

 trim as desired, then dry the end on blotting paper, pour some thick collodion on 

 the holder and press the collodion block down into the collodion. The evapora- 

 tion usually fixes it in two or three minutes, when the holder may be clamped in 

 the jaws of the microtome and the cutting proceed. For collodion sectioning a 

 long, drawing cut is necessary in order to obtain thin, perfect sections. The ob- 

 ject is, therefore, put in the jaws of the microtome at the right level, and the 

 knife arranged so that half or more of the blade of the knife is used in cutting the 

 section. It is advantageous also to have the object with its long diameter parallel 

 with the edge of the knife. The surrounding collodion mass should be cut away, 

 as in sharpening a lead pencil, so that there is not more than a thickness of about 



*The hydrocarbon xylene (C S H 10 ) is called xylol in German. In English, 

 members of the hydrocarbon series have the termination "ene," while members 

 of the alcohol series terminate in "ol." 



t The imbedded object ma}' remain in the castor-xylene clarifier indefinitely 

 without harm. The collodion grows somewhat tougher by a prolonged stay in it. 

 After cutting all the sections desired at one time, the imbedded tissue is returned 

 to the clarifier for future sections. 



