Defects 



PARAFFIN SECTIONS 



123 



Table 1 — {Continued) 



Fig. 77. Block lifts ribbon. 



Possible Causes 



1. Ribbon electrified. (Check by test- 

 ing whether or not ribbon sticks to 

 everything else) 



2. No clearance angle (see Fig. 60) 



3. Upper edge of block has fragments 

 of wax on it (a common result of 2) 



4. Edge of knife (either front or back) 

 has fragments of wax on it 



Remedies 



1. Increase room humidity. Ionize air, 

 either with high frequency dis- 

 charge or bunsen flame a short dis- 

 tance from knife 



2. Alter knife angle to give clearance 

 angle 



3. Scrape upper surface of block with 

 safety-razor blade 



4. Clean knife with xylene 



No ribbon forms 



Defect 



(1) Because wax crumbles 



(2) Because sections, though indi- 



Possible Causes 



vidually perfect, do not adhere 



(3) Because sections roll into cylin- 

 ders 



1. Wax contaminated with clearing 

 agent 



2. Very hard, pure paraffin used for 

 embedding 



3a. Wax too hard at room temper- 

 ature for sections of thickness 

 required 



3b. Knife angle wrong 



Remedies 



1. Re-embed. {Note: Wax very readily absorbs hydrocarbon vapors) - 



2. Dip block in soft wax or wax-rubber medium. Trim off sides before cutting 



3a. Re-embed in suitable wax. If the section is cut very slowly, and the edge of the section 



held flat with a brush, ribbons may sometimes be formed 

 3b. Adjust knife angle 



first, and replacing it with fresh xylene, 

 after about ten or a dozen slides have 

 passed through. It must be remembered 

 that paraffin is insoluble in the alcohol 

 which is used to remove the xylene, so that 

 it is no use soaking a sHde in a solution of 



xylene in wax and imagining that it will 

 be sufficiently free from wax for subse- 

 quent staining. Some people go further 

 than this and have the first two jars con- 

 taining xylene, and then a third containing 

 a mixture of equal parts of absolute alco- 



