Sentence:  These cells were thawed at 37 ` C for 30 min and were deglycerolized by alternately <WSD>centrifuging</WSD> and mixing with descending concentrations of glycerol solutions ( 20 , 18 , 10 , 8 , 4 and 2 % ) . 
Meaning of the word marked with <WSD> tags:  rotate at very high speed in order to separate the liquids from the solids