Sentence:  A study of their activity on thyroglobulin has shown that thyroxine is not preferentially released and that the degradation proceeds stepwise with the formation of macromolecular <WSD>intermediates</WSD> ( Alpers , Petermann and Rall , 1956 ) . 
Meaning of the word marked with <WSD> tags:  a substance formed during a chemical process before the desired product is obtained