SECTIONING 277 



arranged. The settinji; device has a rather wide range of adjust- 

 ment. Sections 10 microns thick are made in general work in 

 microscopic anatomy. The special microtome knife is held in a 

 clamp that can be moved by hand, but must be locked rigidly in 

 place while sectioning. Suppose the setting device is adjusted for 

 sections 10 microns thick, and the wheel is turned. Between the 

 time that the paraffin block passes above the knife edge and then 

 descends to it on the down stroke, the paraffin block has advanced 

 forward exactly 10 microns, but does not advance after the tissue 

 passes below the knife edge. So a section 10 microns thick is cut 

 from the anterior face of the paraffin block each time on the down 

 stroke. However, the ])osition of the paraffin l)lock must be correct. 

 The trimmed end should have the form of a rectangle or square. 

 When the knife is placed in the knife-holder, the back face of the 

 knife should make a slightly acute angle with the plane of the 

 table. The lower edge of the face of the paraffin block should be 

 exactly parallel with the edge of the knife. The knife-holder should 

 be advanced so that the edge of the knife is nearly in contact with 

 the descending block of tissue and then locked. The wheel of the 

 machine is then turned and sections begin to be cut. If conditions 

 are correct, each section will remain with its upper edge just along 

 the front cutting edge of the knife. When the next section is cut, 

 its lower edge will fuse with the upper edge of the previous section 

 because the friction of cutting melts the paraffin along this line. 

 Thus a ribbon of sections is formed. One could cut a ribbon many 

 feet in length. However, it is more convenient to make one about 

 10 inches in length and then transfer this to a shallow paper box. 

 To do this, the outer end is supported with a section-lifter held in 

 the left hand while cutting. When the desired length is cut, the 

 end next to the knife is carefully lifted off with a scalpel or section- 

 lifter and the length of ribbon placed carefully in the paper box. 

 When the next ribbon is cut, it is laid alongside the first in the box 

 and so on, until the desired number of sections are obtained. If 

 one desires to study all parts of an organ, such as the submaxillary 

 gland, it is necessary to save all the ribbon sections and all the 

 sections can be mounted in regular order, thus making a complete 

 series of slides covering the entire microanatomy of that organ. 

 Ribbons of sections stored away in shallow drawers or paper boxes 

 can be kept indefinitely provided they are stored in a cool, dust- 

 proof place. If kept in a warm room or one which becomes very 

 warm on hot summer days, there is a tendency for the thin paraffin 



