Sentence:  In February , 1959 , during the second admission to The New York Hospital , a <WSD>biopsy</WSD> specimen of the left gastrocnemius showed striking increase in the sarcolemmal sheath nuclei and shrunken muscle fibers in several sections . 
Meaning of the word marked with <WSD> tags:  examination of tissues or liquids from the living body to determine the existence or cause of a disease