A Motor-Controlled Device for Slow-Motion Cutting with the Ultramicrotome

The preparation of ultrathin sections of high quality with a Porter-Blum microtome requires that the drive wheel be rotated at a slow, uniform rate during actual cutting. A mechanical device to control the motion of the microtome drive wheel consists of a synchronous motor connected to a drive shaft (4 rev/min), which can be intermittently coupled to the rim of the microtome wheel by a friction drive of 1/2-inch diameter. The microtome drive wheel is rotated manually at a rapid rate until the specimen is about to come into contact with the knife; then the mechanical drive is engaged for slow movement during cutting. When the section has been cut, the drive is disengaged by a lever operated with the left hand; after which, the microtome wheel is turned quickly back to the cutting position with the right hand.     

A Motor-Controlled Device for Slow-Motion Cutting with the Ultramicrotome

The preparation of ultrathin sections of high quality with a Porter-Blum microtome requires that the drive wheel be rotated at a slow, uniform rate during actual cutting. A mechanical device to control the motion of the microtome drive wheel consists of a synchronous motor connected to a drive shaft (4 rev/min), which can be intermittently coupled to the rim of the microtome wheel by a friction drive of 1/2-inch diameter. The microtome drive wheel is rotated manually at a rapid rate until the specimen is about to come into contact with the knife; then the mechanical drive is engaged for slow movement during cutting. When the section has been cut, the drive is disengaged by a lever operated with the left hand; after which, the microtome wheel is turned quickly back to the cutting position with the right hand.     

A Microtome Drive That Gives Either A Fast Cutting Stroke Or A Slow Stroke with Fast Return

The construction comprises a 0.3 hp electric motor, a drive mechanism which transforms the speed of the motor to the two actual cutting speeds, and a clutch mechanism which transmits the slow or the fast movement to the microtome. When the slow cutting speed is used the cam (on the microtome flywheel) and lever mechanism actuates the drive to give a quick return to the cutting position after a slow cutting act. This device, which needs little supervision, has given excellent serial sections, uniform both individually and with respect to others in the ribbon, with all the material on which it has been tested.     

FROZEN THIN SECTIONS OF FRESH TISSUE FOR ELECTRON MICROSCOPY, WITH A DESCRIPTION OF PANCREAS AND LIVER

A simple method has been developed that allows frozen thin sections of fresh-frozen tissue to be cut on a virtually unmodified ultramicrotome kept at room temperature. A bowl-shaped Dewar flask with a knifeholder in its depths replaces the stage of the microtome; a bar extends down into the bowl from the microtome's cutting arm and bears the frozen tissue near its lower end. When the microtome is operated, the tissue passes a glass or diamond knife in the depths of the bowl as in normal cutting. The cutting temperature is maintained by flushing the bowl with cold nitrogen gas, and can be set anywhere from about -160°C up to about -30°C. The microtome is set for a cutting thickness of 540–1000 A. Sections are picked up from the dry knife edge, and are placed on membrane-coated grids, flattened with the polished end of a copper rod, and either dried in nitrogen gas or freeze-dried. Throughout the entire process the tissue is kept cold and does not come in contact with any solvent. The morphology seen in frozen thin sections of rat pancreas and liver generally resembles that in conventional preparations, although freezing damage and low contrast limit the detail that can be discerned. Among unusual findings is a frequent abundance of mitochondrial granules in material prepared by this method.     

Preparing Single or Serial Sections of Calcified Bones and Teeth

An apparatus for cutting single or serial sections of calcified bone and teeth consists of a motor-driven shaft on which is mounted one saw (for single section cutting) or a gang (for serial sectioning at one cutting operation). The plastic-embedded specimen is attached to a cylindrical plastic holder which is in turn mounted on the machine and fed into the saw. Prior to cutting the specimen may be oriented in two planes, as well as rotated, with respect to the cutting edge. Single or serial sections made by means of repeated cuts with a single saw, may be 0.3 mm or more thick as determined by the setting of a micrometer screw. For serially sectioning a tooth or bone specimen at one cutting operation, the thickness of the separators between adjacent saws (0.5 mm or more) determines the section thickness. After sectioning, specimens may be ground and polished, with or without reimbedding in fresh plastic.     

Robust Triboelectric Nanogenerator Achieved by Centrifugal Force Induced Automatic Working Mode Transition

Material abrasion in contact‐based freestanding mode‐triboelectric nanogenerators (FS‐TENGs) seriously deteriorates device mechanical durability and electrical stability, which causes TENGs to be only applicable in the harvesting of mechanical energy at low‐frequency. Here, a wide‐frequency and ultra‐robust rotational TENG is reported that is composed of a built‐in traction rope structure and capable of transforming from contact mode to non‐contact mode automatically as driven by the centrifugal force. With optimizing the fixed x and y position on slider and center shaft, respectively, the mode transition threshold speed can be reduced to 225 rpm. Additionally, the automatic working mode transition TENG exhibits excellent electrical stability, which can maintain 90% electric output after over 24 h of continuous operation, while the contact and non‐contact mode TENGs only retain 30% and 2% output, respectively. The high stability and large output density ensure its usage in the fast and effective charging of commercial capacitors or electronics. This work provides a prospective strategy for rotational TENGs to extend the frequency operation region and mechanical durability for practical applications.     

Vitreous Carbon: A New Material for Making Microtome Knives

The quality of sections obtained by microtomy depends to a large extent on the quality and characteristics of the microtome knife itself. Despite the need for improved microtomy techniques, there have been few significant developments since the introduction of glass and diamond knives in the 1950's. The manufacture of microtome knives from vitreous carbon provides new possibilities for developing both improved methods and improved equipment for specimen sectioning. Vitreous carbon has unique physical properties that lend themselves to the generation of precision cutting edges. Such an edge can be obtained either by breaking a piece of vitreous carbon or by using lapidary techniques. The resultant edge seems well adapted to both thick and thin sectioning. The introduction of vitreous carbon as a sectioning tool offers a significant alternative to metal, glass and diamond knives.     

Contributions to Semithin Sextioning on A Conventional Rotary Microtome

Procedures for obtaining sections 1 μ thick on a conventional rotary microtome are described. Hydrophilic resin blocks with adequate hardness and elasticity for semithin sectioning are made by addition of divinylbenzene and methylmethacrylate to a commercial embedding kit. The blocks are pinched between two simple adapters and mounted in the specimen bolder of a microtome. A glass knife of the Ralph type with an effective blade length of 25 mm is made from a glass slide and attached to a metal bar with paraffin. The low cost assembly is set in the steel knife holder of a conventional rotary microtome. Sections I micron in thickness can be cut from the resin embedded blocks. Staining with the usual staining solutions may be weak due to the thinness of the sections, but the fine resolution and low distortion achieved are compensating gains.     

Cutting Frozen Sections on a Paraffin Microtome

Into a hole drilled in a block of dry ice, a metal microtome object disk is placed to cool. A drop of water is placed on the disk, and the specimen to be cut is fixed in place. By setting the dry ice in a well-insulated box, the specimen is thoroughly frozen. The disk is then clamped in the microtome, and chips of dry ice are wedged between the metal disk and the object clamp of the microtome. This ensures the continued cooling of the specimen while the tissue is being cut.     

Orienting Minute Objects for Sectioning in a Definite Plane

Minute objects can be prepared for sectioning in a definite plane by a method which reembeds them directly on the cutting block under a dissecting microscope. By melting the paraffin immediately around the specimen, the latter can be oriented with reference to the planes of the block. After trimming, the block can be oriented squarely with reference to the microtome knife. Objects as small as 0.2 mm. have been cut successfully. The material sectioned included carpel primordia of Lathyrus, and young embryos, shoot apices and young axillary buds of Pinus. The technic is simpler than most methods previously suggested and it permits good control over the plane of sectioning.     

Contributions to semithin sectioning on a conventional rotary microtome.

Procedures for obtaining sections 1 micrometer thick on a conventional rotary microtome are described. Hydrophilic resin blocks with adequate hardness and elasticity for semithin sectioning are made by addition of divinylbenzene and methylmethacrylate to a commercial embedding kit. The blocks are pinched between two simple adapters and mounted in the specimen holder of a microtome. A glass knife of the Ralph type with an effective blade length of 25 mm is made from a glass slide and attached to a metal bar with paraffin. The low cost assembly is set in the steel knife holder of a conventional rotary microtome. Sections 1 micron in thickness can be cut from the resin embedded blocks. Staining with the usual staining solutions may be weak due to the thinness of the sections, but the fine resolution and low distortion achieved are compensating gains.     

Freezing by Liquid Carbon Dioxide in Making Slides Permanent

The expansion of liquid CO₂ may be employed in a quick-freeze method for making aqueous slide preparations permanent. An apparatus is described for this purpose which could be duplicated satisfactorily by cutting a 22mm square hole in the top of a standard freezing microtome specimen holder. The edges should be filed smooth to provide a flat surface for the slide to rest on, and clamps added to keep the slide in place while freezing. Once the slide is frozen, the cover slip may be readily removed, leaving practically all of the tissue on the slide. Following simultaneous thawing and dehydration of the slide in 95% alcohol, covering is done with Diaphane or Euparal and a clean, dry cover slip.     

Cryostat Techniques: Methods for Improving Conservation and Sectioning of Tissue

Tissues have been conserved for satisfactory enzymatic histochemical assay for up to 12 mo by low temperature storage (in a dry ice chest or at -40° C) and by measures designed to offset the deleterious effects of sublimation of H₂O by using the following modifications of standard procedures (which include steps to give a mechanical support to otherwise fragmenting sections): 1. tissue blocks are coated with a polystyrene solution between each storage period; 2. modified bolts are used as tissue holders and types of bolt holders have been designed to fit on standard microtomes which permit manipulation of each tissue block independently of its mates on the same bolt holder, or the simultaneous cutting of all blocks on any one holder with each advance of the microtome feed; 3. tissues are coated with 20% polystyrene in methylene chloride prior to cutting and rubber cement painted on the slide as an adhesive. Lillie's 20% polystyrene diethylbenzene is used as a mounting medium. Other details of practical importance include the technique of freezing, control of moisture within a cryostat and on the microtome, and tests on histochemical procedures.     

Trimming Selected Areas of Embedments for Electron Microscopy—Dead Simple

Precision trimming of specific areas of plastic embedments can be accomplished without having to find the specimen detail in the block face itself. The desired area is located in a thick section of the pretrimmed block. The position of the area in the section is evaluated using an ocular micrometer. The block is then mechanically trimmed in the ultramicrotome in such a way that the amount of plastic removed from each of its sides is determined from the magnitude of the knife advance. The procedure can be used in connection with inclined blocks if the microtome head can be rotated behind the specimen orientation arc.     

An Inexpensive Microtome Attachment for Cutting 50-Micron Nonfrozen Sections for Electron Microscopic Histochemistry

The attachment is for an American Optical Co., Model 888 freezing microtome. It consists of right-angle bracket made from % inch metal rod, one end of which M clamped in the freezing stage holder; the other supports a tissue holder whose base lies at a right angle to the usual position. The fixed and blotted tissue specimen is enclosed (without infiltration) in parah, on a piece of filter paper which is attached to the base of the tissue holder, and sectioned across its long axis by 50 μ increments. After sectioning, the filter paper is removed from the base, the paraffin matrix opened, and the sections transferred to the appropriate processing fluid     

The Effect Of Temperature and Of Relative Humidity On Sectioning Of Tissues Embedded In Polyethylene Glycol Wax

Experiments carried out in a sealed room, where temperature and humidity could be controlled at will, showed that a high relative humidity in the atmosphere interferes with microtome cutting of tissues embedded in polyethylene glycol wax. The higher the atmospheric temperature the less became the degree of relative humidity which could be tolerated if successful sections were to be obtained.     

A Ralph Knife Holder Assembly for Use with the Sorvall “Porter-Blum” MT-1 Ultramicrotome

The superiority of plastic embedding for the production of high quality sections for light microscopy is well known, but the use of conventional glass knives with a cutting edge of approximately 4 mm has severely restricted the size of specimens in the past. Ralph knives provide a much longer cutting edge and adapters are available for certain models of microtomes and ultramicrotomes. A modified knife holder for use with the Sorvall “Porter Blum” MT-2 microtome was described by Gorycki and Sohm (1979); however, this is not suitable for the MT-1 model. We have therefore designed and made an adapter which enables Ralph knives to be used with this instrument. The design allows approximately 18 mm of cutting edge to be used on each knife, allowing larger specimens to be sectioned than with a conventional glass knife and reducing the frequency with which the knife needs to be changed when working with smaller blocks.     

Interferometric analysis of intrasection and intersection thickness variability associated with cryostat microtomy

Summary Mach-Zehnder interferometric measurements were used to assess the extent of section thickness variability (inter- and intrasection) associated with cryostat microtomy of adrenal sections over a typical working range of 10–20 m. Sections were obtained using a Bright's Cambridge rocking type and a Damon rotary type cryostat microtome to allow comparative analyses. The effective thickness of tissue sections after being mounted onto slides by flash drying was reduced by 90% relative to microtome section thickness setting. A linear relationship between measured thickness and microtome setting was obtained with both instruments. Thickness variability between replicate sections over the range of microtome settings approximated 11% for the rocking microtome and 5% with the rotary microtome. Average intrasection variability was found to be 7% for rocking microtome sections and 4% for sections obtained with the rotary microtome. However, this variability is a negligible source of error in cytophotometric analyses, providing replicate sections are used and an adequate number of measurements are made on mask-delimited individual cells or tissue specimen areas.