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 essentially no iodinated thyroglobulin , a protein that appears to be thyroglobulin has been observed in <WSD>ultracentrifuge</WSD> experiments ( Wolff , Robbins and Rall , 1959 ) . 
Meaning of the word marked with <WSD> tags:  a high speed centrifuge used to determine the relative molecular masses of large molecules in high polymers and proteins