Dynamic Factors in the Formation and Re-absorption of Aqueous Humour.

THE recent article by Duke-Elder and Davsohn,1 discussing the work on aqueous humour dynamics by Kinsey, Grant and Cdgan,2 provides the opportunity for an exchange. of views on this subject; which, I 'believe,. will show that the area of agreement among workers 'in this field is now very much greater than the area still in dispute. There is apparently general agreement that some exchange of constituents occurs between blood and aqueous .by a group 'of processes whichmay be summeAd together as diffusion, and''that superimposed upon this. equilibrating trend there are in addition dyn'am.ic factors which prevent the'.development of co.mplete equilibrium' between blood affd aqueous. Duke-Elder and Davson sum' these. dynamic factors together as secretion.. Kinsey and Grant attempt to sespar-ate the dynamic factors into secretion and. leak. The.problem of determining the factors responsible for these deviations from equilibrium can also be approached from a detailed analysis of the secreting and re-absorbing mechanism, and it is this approach that I have followed. So far as concerns the diffusional exchange between blood and aqueous, the, determining fac.tors must be, on the. one hand the size, mobility, ionic charge, etc., df each component that is exchanged, and on the other hand, the,membrane characteristics or permieabi'lities of the several barriers across which exchange takes place. It seems obvious that these several barriers do not have identical permeabilities. The ciliary barrier is very different fran that in the iris, as has been shown by many investigators. Kinsey and Grant's. hypothesis of a leakage of aqueous into Schlemm's canal is one particularised assumption that the permeability of this portio.n of the blood-aqueous barrier differs from that in the iris and ciliary body. There is, in fact, no reason for assuming that the permeability for each irndividual compone'nt of the aqueousvar,ies in the same fixed proportion in. all the different parts of the blood-aqueous barrier. Kinsey and Grant have. 'measured the rate of tra;nsfer from blood to aqueous of the various components of the intraocular fluid,' and from these measurements have computed co-efficients of transfer for each of'the substances studied. Such computed co-efficients, however,,must represent only averages for