The reaction occurs quickly , and involves {TAIL ~ the addition} of only one reagent to {HEAD ~ a diluted serum specimen} 
The reaction occurs quickly , and involves { TAIL ~ the addition } of only one reagent to { HEAD ~ a diluted serum specimen }
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD