Sentence:  After blotting out most of the saline around the <WSD>sections</WSD> , a drop of * * f was layered over each of the sections , allowed to react for 30 minutes , and then washed with PBS for 15 - 30 minutes . 
Meaning of the word marked with <WSD> tags:  a very thin slice (of tissue or mineral or other substance) for examination under a microscope