Collagenolytic activity in amphibian tissues: a tissue culture assay.

ing from this point of view, one could say that we have built and tested a crude membrane model in which such a phenomenon might be observed, and that thus far the binding energies agree satisfactorily with those calculated from in vivo experiments only when the model contains lipid. In so far as we understand the behavior of the model, it does not permit us to state whether the interactions occur primarily between lipid film and narcotic or between water and narcotic, facilitated by the presence of lipid. In either interpretation, our data suggest that lipid plays an essential role and show that even substances which are not intrinsically surface active can have profound effects when the composition of the interfacial phase is suitably chosen."7 The sensitivity of the model to inert gases and the quantitative similarity of its reactions to their biological effect suggest that further studies of its changes of physical state under narcotics may be very informative.