Microtomes serve to produce thin sections of various samples in the fields of medicine, biology, and botany, materials research, and quality control of engineering materials. These thin sections are produced with knives of different configurations and types. Steel knives made of selected tool steels, manufactured with various types of edge grinding, are known. In addition to these solid regrindable knives, blade-like cutting knives (so-called disposable blades) are widely used. Disposable blades are usually replaced by new ones once their service life has been exceeded. In addition, glass knives and diamond knives are in use for specific applications.
For all types of knife, a plurality of knife carriers and knife holders are known in microtome technology; these additionally differ, in terms of their configuration, depending on the type of microtome for which they are provided. The knife holders that are used perform the principal function of retaining the particular microtome blade in stable fashion in order to achieve the desired sectioning result.
A knife holder having a pressure plate for retaining a blade-like cutting knife is known from DE 44 35 072 C1. The knife holder contains a body and a retaining jaw having an abutment edge on which the back side of the cutting knife rests. The cutting knife is pressed, with the pressure plate, against the retaining jaw. The length of the abutment edge can be greater than the length of the cutting knife. By appropriate positioning of the cutting knife along the abutment edge, a respectively sharper region of the blade cutting edge can be associated with the specimen to be sectioned.
A knife holder for a solid regrindable wedge-shaped steel knife is depicted and described in DE 195 06 837 C1. The steel knife of itself generally exhibits sufficient stability that it is usually retained only in its end regions.
In addition to a stable retaining system that is intended to prevent vibrations at the knife, most knife holders possess devices for setting the relief angle between the knife cutting edge and sample. A device of this kind can be made up, for example, of a circular-segment curved member mounted pivotably on a base, on which member the body of the knife holder is secured. When a user is working with microtomes, the risk always exists of cutting injuries to his or her hand because the blade cutting edge of the microtome knife protrudes from the knife holder. Especially in the context of sample changes, the operator must manually exchange, in the vicinity of the microtome knife, sample cassettes that are located in a clamping system. To avoid injuries, the blade length selected is preferably so short that it does not project laterally from the body. In the retained state, only the blade edge protrudes out of the body. In addition, knife holders can comprise a so-called finger protector. A finger protector of this kind can be made up of a rectangular frame, articulated pivotably on the body of the knife holder, whose bridge joining the two limbs of the U extends, in one end position, over the blade cutting edge and thereby prevents inadvertent contact against the blade cutting edge. A finger protector of this kind may be inferred, for example, from DE 198 24 024 A1.
The risk of injury to the operator is greatest, however, when the maximum service life of the cutting knives has been reached, i.e. they no longer have the sharpness necessary for thin sections and must be replaced. For this, the finger protector must be swung back, the pressure plate must be released, and the microtome blade must be pushed laterally out of the knife holder, using an aid such as a brush handle or the like, until the blade can be grasped with the fingers. To simplify this cumbersome procedure while avoiding the need for assistance from additional aids, in known knife holders the blade length was often selected, specifically in the case where disposable blades were used, so that in the retained state it protrudes to the left and right, but at least on one side, beyond the width of the body with its pressure plate, so as thereby to be more easily graspable. A disadvantage here is that because stable retention is lacking, the microtome knife is not usable in the projecting peripheral region, and this simultaneously constitutes an additional source of risk during the cutting operation and when samples are changed.