DESCARTES, RENÉ DU PERRON (b. La Haye, Touraine, France, 31 March 1596; d. Stockholm, Sweden, 11 February 1650), natural philosophy, scientific method, mathematics, optics, mechanics, physiology.

    drew throughout the rest of his intellectual life. In 1637, for example, Descartes published two important works: Discours de la méthode and Dioptrique. In both he uses physiological ideas from the unpublished Traité at important points in his argument. Specifically, in part V of the Discours, Descartes employs a summary of his cardiovascular physiology to illustrate how the newly discovered laws by which God orders his universe are sufficient to explicate certain of the most important human functions, and the Dioptrique includes a summary of his general theory of sensation as a preliminary to a detailed study of image formation and visual perception. In the 1640's, too, Descartes drew heavily upon the unpublished Traité. The complicated arguments of the Passions de l'âme, published near the end of that decade, rest firmly on the extensive survey of basic Cartesian physiology incorporated in part I, while Descartes's unruffled assertiveness in his correspondence and later philosophical writings on the “beast-machine” makes full sense only against a background provided by the Traité's automaton.

Descartes, however, had left one major physiological problem untreated in the Traité: the reproductive generation of animals and men. He had insisted for reasons of methodological circumspection that the homme of the Traité was directly contrived by God. The Cartesian program, of course, was to explain all but rational, deliberately willful, or self-conscious behavior in terms of mere mechanism. He had eliminated the souls, principles, faculties, and innate heats of traditional physiology and had systematically replaced them with hypotheses and analogies of purely physical nature. But generation had escaped, and its explanation in mechanistic terms was clearly needed for the logical completion of his system. Recently proposed theories of animal generation had left the subject replete with Galenic faculties and Aristotelian souls, and even William Harvey was soon to show himself content with innate principles and plastic forces as the controlling agents of embryonic development. Descartes, to be consistent, could not accept these explanatory devices and had, therefore, to formulate some alternative.

His correspondence and certain manuscript remains show that Descartes had actually been deeply concerned with the problem of animal generation for a considerable period of time. Earliest references in the former occur in 1629, and snippets of the latter reveal fitful grapplings with the problem, some of them even leading to direct anatomical investigations undertaken, apparently, as a means for providing clues to the processes involved. Descartes's ideas on the subject really seem to have crystallized, however, in the late 1640's, when he triumphantly announced his “solution” to the long-plaguing problem in a series of enthusiastic letters to Princess Elizabeth. The ideas alluded to in these letters appear to be those published as the De la formation du foetus, which Descartes completed not long before his death.

First published by Clerselier in 1664, the Formation is a curious essay. Unlike the Traité de l'homme, which much preceded it in date of composition, the Formation consists mainly of bald assertions and only the vaguest mechanisms. Generation commences when the male and female seeds come together and mutually induce a corpuscular fermentation. The motion of certain of the fermenting particles forms the heart, that of others the lungs. Streaming of particles as the process continues furrows out the blood vessels; later, membranes and fibers are formed which ultimately weave together to construct the solid parts. The formation of the bodily parts is described in these vague terms (no mechanism of organ or vascular development is ever made more precise than this), yet Descartes apparently felt satisfied with his results. For by describing generation in chemical and corpuscular, rather than vital or teleological, terms Descartes had, at least in his own mind, completed the mechanistic program for physiology. Everything in the animal's life, from its first formation to its final decay, now had an automatic, mechanical explanation.

The impact of the Cartesian physiological program, once it was publicly known, was enormous. In two ways—philosophically and physiologically—Descartes transformed long-standing beliefs about animals and men. Philosophically, of course, his notions of mind-body dualism and animal automatism had extremely important implications that were not lost on Henry More, Malebranche, Spinoza, and Leibniz, along with many others in the seventeenth century. The “beast-machine” idea also had continuing ramifications in the eighteenth century, leading, at least according to Aram Vartanian, directly to La Mettrie's L'homme machine. Also, according to Vartanian, Descartes's posthumously published views on human function and animal generation exerted important philosophical influence, contributing greatly to the eighteenth-century concern with these biological subjects by many of the philosophes. But physiologically, too, Descartes's conceptions had an impact that in many ways was even more impressive than the philosophical influence, because it affected the actual course of contemporary science.

Almost as soon as Descartes published his Discours de la méthode, a few professors of medicine began to react to specific Cartesian physiological ideas and to the general Cartesian program. Plempius at Louvain