Method IX 59 



The pieces may remain in the clearing fluid two or three 

 days without serious injury. It is better to section immediately. 



5. To section and mount. — (12) Use a sliding microtome such 

 as the Thoma. Set the knife obliquely, so that, in making the 

 section, the stroke will involve two or three inches of the edge. 

 Fasten the block in the object-carrier with the piece of tissue 

 arranged so that its longest horizontal diameter is parallel to the 

 edge of the knife. Keep the knife and the block flooded with 

 the clearing fluid and make sections 50-100 micra thick. Sec- 

 tions can be made much thinner, but for general purposes it is 

 best to have them thick enough to include as much of the neu- 

 rone as possible and at the same time allow enough light to 

 examine it. 



In making sections of the cerebral cortex, e.g., the plane of 

 the section should be perpendicular to the surface of the cortex 

 or parallel to the long axis of the pyramidal cells. 



The sections cut much better in clearing fluid than in alcohol, 

 which is generally used for celloidin sections and, at the same 

 time, they are either cleared or are clearing in the fluid prepara- 

 tory to mounting. Handle the sections with a camel's hair 

 brush. Transfer them from the knife to the slide and keep them 

 there flooded with the clearing fluid until examination under the 

 microscope shows them to be thoroughly cleared. Several slides 

 of sections may be cut before any are mounted. 



{b) To mount, discard such sections as examination has proved 

 to be undesirable, arrange the remainder in position, remove the 

 clearing oil and press the sections down to the slide by blotting 

 them with several thicknesses of filter paper. Then with a 

 pipette flood the sections with pure xylol for about five minutes 

 to replace the oil in the sections, xylol being more miscible with 

 the balsam which is to follow. Remove the xylol by again press- 

 ing several layers of filter paper over the sections and immediately 

 place on enough thick Canada balsam or, better, colophonium 

 (II, E, p. 21) to make a complete layer over them, and, without 

 using a cover-glass, lay the preparations level in a warm, dry 

 place, free from dust, to allow the balsam to harden. 



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