Trimming the Block

This is by far the easiest section to deal with and it is recommended that blocks should be trimmed to this shape whenever possible. Dimensions are not critical, but a width of 4 mm and a length of 12 imn is probably adequate in most cases. 

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Trim the block into a trapezoid and prepare 4-8 p,m sections with a microtome according to standard procedures. 

After 15 min, trim the block, section the block and collect sections onto warm subbed slides or coverslips coated with Histostik (Accurate Chemical and Scientific, Co.) with standard methods. 

Secure the block in a microtome chuck or small vice. Using single-edge razor blades, carefully trim the block down to a suitable block face for sectioning. This is typically a trapezoid ranging in size from about 0.2-1.0 mm on each side. 

Trim the block around the preparation using a surgical carbon-steel razor blade cleaned with acetone to approximately 2.5 x 1 mm and until the desired segment to be sectioned is reached. 

Once a desired region to be sectioned is identified, trim the block further (to 0.5 X 0.5 mm) using an acetone-cleaned, stainless-steel Teflon-coated blade. 

Sectioning material for immunocytochemistry with glass and diamond knives is identical to the process used for conventional EM. One difficulty frequently encountered is that unosmicated tissue embedded in plastic is sufficiently cleared by the solvent and embedding process as to be almost invisible. This makes orientation of the tissue in the trimming of the blocks difficult and increases the chances of mistakes of cutting too much. A small amount of Sudan Black dye can be added to... 

Trim and peel the blocks from the slides with razor blades and forceps. 

The whole tissue processing from fixation to embedding in paraffin can be performed manually or automated by means of processing machines. Cutting of paraffin-embedded tissues is performed by means of microtomes. Trimmed paraffin blocks are cut at 3 10 pm (5 pm is commonly used). 

The lithium should be added in the form of very small pieces. The pieces are most conveniently prepared as follows. Trim the oxide layer off a small block of lithium metal under mineral oil, grip it with tweezers and rinse the mineral oil off in a beaker of dry ether. Hold the block in the ether vapors momentarily to dry, and then plunge it into a tared beaker of mineral oil for weighing. Cut the block into strips with a sharp knife, remove the pieces one by one, and squeeze them into long flat ribbons with pliers which are frequently dipped into the mineral oil. Cut the ribbons into short sections over another beaker of dry ether, swirl and transfer the pieces to a third beaker of ether to wash off the last traces of mineral oil before adding the lithium to the reaction flask. 

The block with the tissue section is trimmed and ultrathin sections are cut with an ultramicrotome. The enzyme product may be hazardous for diamond knives, so that normal glass knives should be used. 

The amplifier (5) boosts the signal, eliminates temperature coefficients, and adjusts the offset. The low pass filter (6) limits the bandwidth. The drive circuit is a closed loop system to achieve a stable drive oscillation. It consists of a structure (not drawn) that detects the oscillation movement of the drive of the yaw-rate sensor element, a control unit (2), and an actuator (not drawn). The start circuit (9) initiates the drive oscillation at power on. The block (8) generates all necessary adjustment signals and includes the logic circuit for the trim and an EPROM (erasable programmable read-only memory) for the storage of the trim data. 

Trim the top, bottom, and sides so that a small amount of frozen O.C.T. is surrounding the tissue. With a single edge razor blade, shave off a couple of millimeter at a time and cut perpendicularly to remove the shavings if necessary (Fig. 4.4c, d). Do not trim the face of the block with the razor blade. 

Fig. 4.4 Cryostat. Use a cryostat to cut sections from tissue frozen on a chuck, (a) The chamber of a cryostat with the frozen tissue indicated by the black arrow. This tissue was frozen in a rectangular mold, (b) The chuck with the tissue is placed in the arm. (c) The excess O.C.T. is trimmed off with a razor blade by cutting into the block several times, (d). The trimmed frozen O.C.T. is removed with a razor blade cut from the top of the block, (e) The knife is adjusted into position very close to the block, but not touching. The block is advanced toward the block until sections are cut. (f) The anti-roU plate prevents cut sections from curling, (g) An alternative to the anti-roll plate is to use a fine paint brush to hold a section as it comes off the block, (h) Sections are picked up on microscopes slides, (i) Lower the bottom of the slide until the section attaches then warm the slide, (j) When the section is dry, remove the dried film of O.C.T. arrows) with a forceps. Note the two rows of sections toward the slide label down) have the film already removed...

Trim the snrface of the tissue block and subject to thin-sectioning on an ultramicrotome. 

Sections fail to ribbon. Room temperature too high—turn on air conditioning or seek alternative venue. Block poorly trimmed—use a sharp blade to retrim and align sides of the block. 

The trimmed tissue blocks were immediately frozen in powdered dry ice, which allows tissues to be frozen without cracks, and stored at -80°C until use. 

Nascent mRNA. This may be a pro-mRNA that is formed in the nucleus as a precursor, then combines with some protein in the nucleus as a stage in its passage to the cytoplasm. This intermediate mRNA may be equivalent to silent mRNA. Included in this concept are special transport proteins, and special endonucleases for trimming the nascent mRNA into a translatable form of mRNA. A repression at this stage might represent a block in the conversion of nascent to translatable mRNA. 

Fig. 3. Orientation of the sample. A. The sample map (arrow). B. The position of the block before (thin arrow) and after (thick arrows) the detachment from the cover slip. C. The sample before its trimming the external view of the block. D. Scheme of the grid and the position of the cell (green, thick arrow) and cavities (circles, thin arrows). The cavities should form a horizontal line (red broken line). E. Position of the pyramid. F. The position of the sample after the orientation and trimming of the upper and lower edges (thick arrows) of the sample. The cell of interest is shown by the double arrow. The small arrow indicates the position of the glass knife related to the pyramid.

Advance knife holder and trim the fiont of the block in 1 jmi sections. The initial trimmings will be sucrose and will be crumbly. It is usually easy to see when the tissue is being sectioned. 

Select a suitable area for thin sections and trim the sides of the block. This can be done on the sides of a glass knife or with a diamond trimming tool. The smaller the block the more likely it is to section well. 

Chert. A general term for a cryptocrystalline siliceous rock that may occur in either nodular or tabular form. Chert stones were used as pavers and runners in the old paddle type of mill for grinding potters materials trimmed chert blocks are now used as a lining material for ball mills. 

The length of time the soap should remain in frames is dependent on the quality, quantity, and season or temperature, and varies usually from three to seven days. When the requisite period has elapsed, the sides and ends of the frames are removed, and there remains a solid block of soap weighing from 10 to 15 cwt. according to the siise of frame used. The blocks, after scraping and trimming, are ready for cutting into slabs. 

Glass knives are used to face the block up to the specimen and for final trimming either in the... 

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