Journal of Applied Microscopy. 



87 



THE CUTTING OF PARAFFIN SECTIONS. 



The Position of the Knife.— I usually 

 place the knife at an angle of about 30" 

 to 35° to the microtome. I believe sec- 

 tions are cut more easily with the knife 

 in this position, than when the knife is 

 placed at right angles to the microtome, 

 as is often recommended, and it does 

 not seem to me that the tissues suffer 

 materially from distortion, when they 

 are cut with the knife at an angle, as is 

 sometimes claimed. 



Section Cutting. — In the last article of 

 this series the method of imbedding 

 sections in paraffin was described, and 



clamped in the microtome. This is done 

 in such a way that the paraffin block 

 just escapes the knife when drawn 

 beneath it. A number of rather thick 

 sections (20 to 40 microms) are cut 

 by moving the micrometer screw from 

 right to left four to eight notches every 

 time the knife has been drawn over the 

 paraffin block and has been brought 

 back again, until it is noticed that the 

 knife touches all parts of top of the 

 paraffin block, or until the tissue is 

 fairly exposed. The sections may now 

 be saved, and it may perhaps be well 

 to state that it is better not to try and 

 cut very thin sections to begin with; 



Fig. 2. 



it may be remembered that after thor- 

 ough impregnation of the tissues with 

 the paraffin had been discussed, direc- 

 tions were given for blocking the tis- 

 sues in paraffin by means of the imbed- 

 ding L's. Before fastening the paraffin 

 blocks into the clamp on the microtome, 

 preparatory to cutting sections, the 

 paraffin is trimmed with a sharp knife 

 from the end of the paraffin block, until 

 the tissue is exposed, care being taken, 

 however, to leave a flat surface. The 

 top of the paraffin block is then beveled 

 off on three sides to within a very short 

 distance of the tissue. The fourth side, 

 that which faces the knife when the 

 block is clamped in the microtome, 

 should be trimmed only to within about 

 one-eighth of an inch of the tissue. This 

 «dge of paraffin is made use of, as will 

 be seen in a moment, for preventing the 

 sections from curling while they are cut. 

 The paraffin block is now ready to be 



sections twenty to fifteen microms in 

 thickness will answer very well. To 

 begin with then, the milled head of the 

 micrometer screw is turned four notches 

 from left to right, then the knife is 

 drawn over the block with a steady, 

 even pull and without using undue pres- 

 sure. Usually the sections will curl up 

 as they are being severed from the 

 paraffin block. This may very readily 

 be prevented by holding the tip of a 

 camel's hair brush, which has been 

 pointed by drawing it between the lips, 

 against the edge of the section, as soon 

 as it begins to curl. A little practice 

 will enable one to do this almost auto- 

 matically. The sections are transferred 

 to a paper by means of the camel's-hair 

 brush, which process is facilitated if the 

 brush has been slightly moistened with 

 saliva, as the_ section will then adhere 

 lightly to the brush. 



