103 



clarification. In such cases the process may be hastened by placing 

 the tissue in the clarifier in a warm place, and changing the clarifier 

 several times. If the block still remains opaque, remove to 95% 

 alcohol for a day for dehydration, pass through chloroform, and into 

 clarifier. In this way the mass may usually be cleared perfectly. 

 Change the clarifier to fresh after the first and second days. The 

 sectioning may be done after a few hours' immersion, although a 

 several days' clarification is preferable.* 



If a paper box were used, after the collodion is hardened and 

 clarified, remove the paper box, absorb the castor-xylene on the sur- 

 face, trim the end and put some fresh, thick collodion on the cork or 

 other holder. Press the block firmly against the holder ; within two 

 minutes it will be firmly cemented and one may proceed at once to 

 clamp the holder in the microtome and commence cutting ( 57). 



57. Cutting the sections. For collodion sectioning, a long 

 drawing cut is necessary in order to obtain thin, perfect sections. 

 The knife should, therefore, be set at an obliquity of 15-20* or less, 

 so that half or more of the blade is used in cutting the section. Re- 

 call that in the paraffin method the knife is set at right angles to the 

 direction of the cut, and the stroke is a rapid straight one. Trim 

 away the surrounding collodion mass, as in sharpening a lead pencil, 

 so that there is not more than a thickness of about two millimeters 

 all around the tissue, being careful, however, to leave a broad base 

 as a support to the tissue and prevent its bending under the impact 

 of the knife ; if the collodion mass is too tapering, bending will 

 occur and thin sections cannot be cut. 



Clamp the object in the jaws of the microtome, placing it so that 

 the mass of collodion is opposite the side to which the pressure of the 

 knife is applied in cutting. It is advantageous also to have the ob- 

 ject placed with its long diameter parallel with the edge of the knife. 



When knife and tissue are properly arranged wet the tissue 

 well with clarifier and flood the knife with the same. Make the 

 sections with a slow, steady motion of the knife. With a small ob- 

 ject (3x5 mm.) and a good sharp knife, sections 5jw to 6yu can be cut 

 without difficulty. In addition to a sharp knife, however, there are 



*The imbedded object may remain in the castor-xylene clarifier indefi- 

 nitely without harm. The collodion grows somewhat tougher by a prolonged 

 stay in it. After cutting all the sections desired at one time, the imbedded tis- 

 sue is returned to the clarifier for future sectioning. 



