Next to Darwin, though by a wide interval, August Weismann (d. 1914, _a.e._ 80) has most influenced general biological thought. His failing eyesight at middle age caused him to abandon the microscope for biological thinking, a field where there was a great need of synthesis and expert theory and in which he developed great power and influence. His hierarchy of metamicroscopic vital units, his dogma of the non-inheritance of acquired qualities in confutation of the prevailing Lamarckianism, and his demonstration of the continuity of the germ plasm have been theses of great interest and centers of very active discussion, even outside the special field of zoölogy, although in the latter doctrine, which chiefly concerns this discussion, he was in a sense anticipated by Owen, Jäger, Nussbaum, and especially by Sir Francis Galton, as he later found.[164] He first set forth the now generally accepted view that most of the primitive unicellular organisms do not die and also sought to explain how death first entered the world.[165] He says: We cannot speak of natural death among unicellular animals, for their growth has no termination which is comparable with death. The origin of new individuals is not connected with the death of the old; but increase by division takes place in such a way that the two parts into which an organism separates are exactly equivalent, one to the other, and neither of them is older nor younger than the other. In this way countless numbers of individuals arise, each of which is as old as the species itself, while each possesses the capability of living on indefinitely by means of division.