Techniques are described for collecting newly formed aqueous humour from the ciliary body of the eye, and for collecting newly formed CSF directly from the choroid plexus of the anaethetized cat. Both these two fluids were found to have a little lower concentration of K than plasma ultrafiltrate but did not so much differ from plasma ultrafiltrate in Cl. Na concentrations of these fluids were higher than expected in an ultrafiltrate.Most striking feature is the finding that less Mg in the newly formed aqueous humour and more Mg in the newly CSF than plasma ultrafiltrate. Ca in these two fluids were lower than plasma ultrafiltrate. The change of each electrolyte concentration along the course of aqueous circulation and CSF circulation was also reported. The fact that the destribution ratio across barrier was taken as evidence that the mechanisms involved in cation transfer are quite selective. Though not proven, active transport was considered the most likely explanation of these findings.It is postulated that the further modification of aqueous humour and CSF electrolyte pattern from the initial forming site to their circulation course may the result of the same mechanisms residing in cells of similar origin as those of ciliary body and choroid plexus, but the both of them are somewhat different each other at the blood-aqueous barrier and blood-CSF barrier.
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