Page "Countercurrent exchange" Paragraph 38

In the example image water enters at 299 mg / L ( NaCL / H < sub > 2 </ sub > O ).

Water passes because of a small osmotic pressure to the buffer liquid in this example at 300 mg / L ( NaCL / H < sub > 2 </ sub > O ).

Further up the loop there is a continued flow of water out of the tube and into the buffer, gradually raising the concentration of NaCL in the tube until it reaches 1199 mg / L at the tip.

The buffer liquid between the two tubes is at a gradually rising concentration, always a bit over the incoming fluid, in our example reaching 1200 mg / L.

This is regulated by the pumping action on the returning tube as explained immediately.