Sentence:  Whether this abnormal TSH differs chemically from pituitary TSH , or is , alternatively , normal TSH with its period of effectiveness modified by some other <WSD>blood</WSD> constituent , cannot be decided without chemical study of the activity in the blood of these patients and a comparison of the substance responsible for the blood activity with pituitary TSH . 
Meaning of the word marked with <WSD> tags:  the fluid (red in vertebrates) that is pumped through the body by the heart and contains plasma, blood cells, and platelets