The water permeability of basement membrane under increasing pressure: evidence for a new theory of permeability

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Abstract
The egg of the ichneumon wasp Nemeritis canescens is known to be resistant to the defence reactions of its usual host, Ephestia kuehniella, by virtue of a coating on its surface. The coating is here shown also to endow Nemeritis with resistance to the defence reactions of Achroia grisella and, by implication, several other species of hosts. Three ways in which the coating might act are: (1) passively, by mimicking the lining of the haemocoele; (2) indirectly, by preventing the modification of substances in the haemolymph; (3) directly, by inhibiting the adhesion of blood cells. Mimicry of the host's internal lining is ruled out by experiments showing that the blood cells of Ephestia react to the internal lining of Achroia, and vice versa, although neither host reacts to Nemeritis. The idea that the coating might prevent modification of substances in the plasma, and so indirectly inhibit encapsulation, is not completely eliminated; but several experiments provide no evidence for it, and several observations favour a hypothesis of direct action by the particles on the blood cells. The nature of that direct action is inconclusively examined. Preliminary experiments suggest that the particles dissociate the cells of young capsules of Ephestia and may, therefore, act to inhibit the adhesion of cells to form capsules. Cells of capsules formed in Tenebrio molitor, which always encapsulates Nemeritis, were not dissociated; which indicates that this mode of action has the required element of specificity. The possibility that substances chemically similar to the particles of Nemeritis might inhibit cell adhesion and aggregation in vertebrates is briefly discussed.