Sentence:  We are therefore driven to the conclusion that the proteid food is split into a urea <WSD>moiety</WSD> and a fatty <WSD>moiety</WSD>, that the urea <WSD>moiety</WSD> is at once discharged, and that such of the fatty <WSD>moiety</WSD> as is not made use of directly by the body is stored up as adipose tissue. 
Meaning of the word marked with <WSD> tags:  A specific segment of a molecule.