Looking for books on embryology? Check our section of free e-books and guides on embryology now! This section contains free e-books and guides on embryology, some of the resources in this section can be viewed online and some of them can be downloaded. Microtomes use steel, glass, cutting edge anatomy pdf download diamond blades depending upon the specimen being sliced and the desired thickness of the sections being cut.
Industrial grade diamond knives are used to slice hard materials such as bone, teeth and plant matter for both light microscopy and for electron microscopy. A diagram of a microtome drawn by Cummings in 1770. It was found that to observe the structure of the specimen under observation it was important to make clean reproducible cuts on the order of 100 µm, through which light can be transmitted. This allowed for the observation of samples using light microscopes in a transmission mode. One of the first devices for the preparation of such cuts was invented in 1770 by George Adams, Jr. The device was hand operated, and the sample held in a cylinder and sections created from the top of the sample using a hand crank. In 1835, Andrew Prichard developed a table based model which allowed for the vibration to be isolated by affixing the device to the table, separating the operator from the knife.
The apparatus has enabled a precision in work by which I can achieve sections that by hand I cannot possibly create. Namely it has enabled the possibility of achieving unbroken sections of objects in the course of research. Several sources describe the Purkyne model as the first in practical use. The obscurities in the origins of the microtome are due to the fact that the first microtomes were simply cutting apparatuses, and the developmental phase of early devices is widely undocumented. At the end of the 1800s, the development of very thin and consistently thin samples by microtomy, together with the selective staining of important cell components or molecules allowed for the visualisation of microscope details. Today, the majority of microtomes are a knife-block design with a changeable knife, a specimen holder and an advancement mechanism.
In most devices the cutting of the sample begins by moving the sample over the knife, where the advancement mechanism automatically moves forward such that the next cut for a chosen thickness can be made. The section thickness is controlled by an adjustment mechanism, allowing for precise control. The tissue is then cut in the microtome at thicknesses varying from 2 to 50 µm. The ultramicrotome is also used with its glass knife or an industrial grade diamond knife to cut survey sections prior to thin sectioning. These survey sections are generally 0. 5 to 1 µm thick and are mounted on a glass slide and stained to locate areas of interest under a light microscope prior to thin sectioning for the TEM. Thin sectioning for the TEM is often done with a gem quality diamond knife.
Complementing traditional TEM techniques ultramicrotomes are increasingly found mounted inside an SEM chamber so the surface of the block face can be imaged and then removed with the microtome to uncover the next surface for imaging. These microtomes have heavier blades and cannot cut as thin as a regular microtome. Technique: thin polymer sections are needed in order that the infra-red beam will penetrate the sample under examination. It is normal to cut samples to between 20 and 100 µm in thickness.
Fluorescence microscopy: samples can be made into thin slices to be viewed under a fluorocent microscope. This method is contact-free and does not require sample preparation techniques. The laser microtome has the ability to slice almost every tissue in its native state. Depending on the material being processed, slice thicknesses of 10 to 100 µm are feasible.
The Compresstome uses a specimen syringe or “lipstick-like” tube to hold the tissue. The tissue specimen is completely embedded in agarose, and the tissue is slowly and gently pressed out of the tube for the vibrating blade to cut. The device operates in the following way: the end of the specimen tube where the tissue emerges is slightly narrower than the loading end, which allows gentle “compression” of the tissue as it comes out of the tube. The slight compression prevents shearing, uneven cutting, and vibration artifacts from forming. Note that the compression technology does not damage or affect the tissue being sectioned. Modern sled microtomes have the sled placed upon a linear bearing, a design that allows the microtome to readily cut many coarse sections. By adjusting the angles between the sample and the microtome knife, the pressure applied to the sample during the cut can be reduced.