Aristotle's Psychology: On the Soul and Parva Naturalia

on indefinitely, because they lack organs for maintaining life. As we go up the scale of living forms, this diffusion of soul throughout the body becomes less and less marked; the higher the order of life the greater the centralization. In the case of animals, the body consists generally of three main divisions: the head, thorax, and abdomen. Aristotle points out1 that if a wasp’s head is cut off, the thorax and abdomen continue to live for a time; if the abdomen is cut off, the head and thorax continue to live. In other words, the part which is conjoined with the thorax exhibits this continuance of vitality. For this reason it would appear that the anatomical centre is also the life-centre. This is, furthermore, on a priori from theoretical principles grounds the best and most advantageous position. It is reasonable to suppose, therefore, that nature in her wise economy2 has employed this central section as the vital centre.

This view, however, is not merely derivable from rational considerations, but is also supported by grounds of observation. The life-centre may be localised not only in the thoracic region, but specifically in the heart. For this statement Aristotle adduces the following arguments: (1) disease of the heart is the most rapidly and certainly fatal; (2) psychical affections, such as fear, sorrow, and joy cause an immediate disturbance of the heart; (3) the heart is the part which is first formed in the embryo, and, as he says in the History of Animals,3 it appears in the egg of the chicken on the third day of incubation as a red spot (the

1 De juvent. On Youth, Old Age, Life and Death, and Respiration 468a 21; De part. anim. On the Parts of Animals 667b 22; De respir. On Respiration 479a 5.
2 Cf. Leibniz’s "choice of Wisdom," Princ. 11; also Nouv. Ess. II., ch. xxi, 13, Langley’s translation, p. 183.
3 Hist. anim. History of Animals 561a 6-12.