In ordinary cases possible changes in the concentrations only affect the electromotive force by a few parts in a hundred, but, by means such as those indicated above, it is possible to produce such immense differences in the concentrations that the electromotive force of the cell is not only changed appreciably but even reversed in direction.
A general nerve-plexus probably exists over considerable parts of the skin, and there are special nervous concentrations in the region of the epistome and along a double crescent (N) which follows the parietal attachment of the coelomic septum.
Porcelain, enamelled iron, for high concentrations even cast-iron without any protection, are also in use.
Mainly agricultural, and in parts purely feudal, was changed into one of vast industries and of great concentrations of population; and for the ferment created by this change there was no such safety-valve in the representative system as had existed in England since the Reform Bill.
Pfeffer showed that certain substances in definite concentrations cause the tips of hyphae to turn towards them; other substances, though not innutritious, repel them, as also do nutritious bodies if too highly concentrated.