- The alimentary canal in Scorpio, as in Limulus, is provided with a powerful suctorial pharynx, in the working of which extrinsic muscles take a part.
Thus the field of disease arising not from essential defect in the body, but from external contingencies, is vastly enlarging; while on the other hand the great variability of individuals in susceptibility explains the very variable results of such extrinsic causes.
Evidence is accumulating which may end in the explanation and perhaps in the prevention of the direst of human woes - cancer itself, though at present inquiry is being directed rather to intrinsic than to extrinsic causes.
Accordingly, in 1655, he printed everything that had passed between them (under the title of A Defence of the True Liberty of Human Actions from Antecedent or Extrinsic Necessity), with loud complaint against the treatment he had received, and the promise added that, in default of others, he himself would stand forward to expose the deadly principles of Leviathan.
This trophic influence which one neuron exerts upon others, or upon the cells of an extrinsic tissue, such as muscle, is exerted in that direction which is the one normally taken by the natural nerve impulses.