Sentence:  There is some reason to think that thyroglobulin synthesis may proceed independently of iodination , for in certain transplantable tumours of the rat thyroid containing <WSD>essentially</WSD> no iodinated thyroglobulin , a protein that appears to be thyroglobulin has been observed in ultracentrifuge experiments ( Wolff , Robbins and Rall , 1959 ) . 
Meaning of the word marked with <WSD> tags:  in essence; at bottom or by one's (or its) very nature