Sentence:  ( 2 ) The conjugates as well as the intermediate sera were absorbed for 30 minutes with 20 - 50 mg of <WSD>proteins</WSD> extracted from healthy sweet clover stems . 
Meaning of the word marked with <WSD> tags:  any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes