A fresh supply of {TAIL ~ solution} to the face of {HEAD ~ the membrane} is provided by a stirrer 
A fresh supply of { TAIL ~ solution } to the face of { HEAD ~ the membrane } is provided by a stirrer
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH