CH. VII '] COLLODION SECTIONING 177 



containing more than two to three cubic centimeters is placed in 40 or 50 cc. of 

 the picric-alcohol and left 6 to 24 hours, when the first picric-alcohol should be 

 thrown away and fresh added. After one or two days more the picric- 

 alcohol should be poured off and 67% alcohol added. In a day or two this is re- 

 placed by 75% or 82% alcohol ; 82% is on the whole most satisfactory, and the 

 tissue may be left in this till it is ready for dehydration. 



\ 26S. Dehydration before Infiltration. — When one is ready to imbed for 

 sectioning, the tissue must first be dehydrated in plenty of 95% or stronger alcohol. 

 It is better to take only a small piece for this. The smaller the piece the thinner 

 the sections that may be made. The dehydration will usually be completed in 2 to 

 24 hours. If the alcohol is changed two or three times the dehydration will be 

 hastened. 



\ 269. Saturating with Ether- Alcohol. (f 322). — The next step is to remove 

 the tissue from the alcohol and place it in a vial of ether-alcohol (J 322) for 2 to 

 24 hours. The dehydration becomes somewhat more complete by this step, and 

 the tissue is more perfectly prepared for the reception of the collodion. If the 

 dehydration is very thorough in the alcohol, this step may be ommitted, however, 

 but one is surer of success if the ether-alcohol is used. 



\ 270. Infiltration with Thin Collodion. — The ether-alcohol is poured off, 

 and a mixture of thin collodion is added (§ 319). Two or 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. 



\ 271. Infiltration with Thick Collodion. — The thin collodion is poured off 

 and thick collodion {\ 319) 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 

 of a day or even a week is more certain to insure a perfect infiltration. 



§ 272. Imbedding. — The tissue may be imbedded in a paper box, such as is 

 used for paraffin imbedding, or in any of the other boxes devised for paraffin. It 

 is better, if paper is used, to put a small amount of oil on the paper to prevent 

 the collodion from sticking to it. Vaselin spread over lightly and then re- 

 moved, so far as possible, with a cloth or with lens paper, gives the right surface. 

 For small objects 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. 

 143). The vial should contain sufficient chlorform 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 advantageous 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 



