Sentence:  Moreover , after concentration using negative <WSD>pressure</WSD> dialysis , agglutinin activity could sometimes be detected in the region designated 2a ( donors P. J. , D. A. , and J. F. , Fig. 1 ) . 
Meaning of the word marked with <WSD> tags:  the force applied to a unit area of surface; measured in pascals (SI unit) or in dynes (cgs unit)