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.

    of the animals come about”; thus one can also explain “how in ourselves all those operations occur which [we] perform without any aid from the reason.” Closely associated in the Regulae with this notion of animal automatism was Descartes's belief that human sensation is a two-step process consisting, first, of the mechanical conveyance of physical stimuli from the external organs of sense to a common sensorium located somewhere in the body and, second, of the internal perception of these mechanically conveyed stimuli by a higher “spiritual” principle.

Implicit in these two notions and seeming to tie them together is the assumption, evident in broader compass but in as terse a formulation as elsewhere in the Regulae, that all phenomena of the animate and inanimate world, with the sole exception of those directly connected with human will and consciousness, are to be explained in terms of mathematics, matter, configuration, and motion.

The fuller working out of his physiological ideas occupied Descartes in the early 1630's, when he was concerned generally with the development of his ontological and methodological views. In 1632 he several times referred to physiological themes and projects in his correspondence, and in June he informed Mersenne that he had already completed his work on inanimate bodies but still had to finish off “certain things touching on the nature of man.” The allusion here was to the Traité de l'homme, which with the Traité de lumière was meant to form Le monde. Along with the Traité de lumière, however, the Traité de l'homme was suppressed by Descartes after the condemnation of Galileo in 1633, and although it thus had to await posthumous publication in the 1660's, his writing of the Traité de l'homme proved extremely important in the further maturation of Descartes's physiological conceptions.

The Traité de l'homme begins and ends with a proclamation of literary and philosophical license. In the Traité, Descartes writes, we deliberately consider not a real man but a “statue” or machine de terre expressly fashioned by God to approximate real men as closely as possible. Like a real man, the machine de terre will be imagined to possess an immaterial soul and a physical body, and, also like a real man, its physical body will consist of a heart, brain, stomach, vessels, nerves, et al. But since we are considering only an artificial man—a contrivance fashioned more perfectly but on the same principles as a clock or water mill—we will not be tempted to attribute the motions and activities of this man to special sensitive or vegetative souls or principles of life. Nothing more than a contained rational and immaterial soul and “the disposition of organs, no more and no less than in the movements of a clock or any other automaton” will be needed to comprehend the active functioning of this special contrivance formed by God and operated thereafter by the principles of mechanical action. We are to bear in mind, of course, that the man of the Traité is remarkably like men we know, but our literary and philosophical license allows us to hypothesize and analogize freely.

Descartes fully exercises his self-proclaimed license in the rest of the Traité. He first surveys various physiological processes, giving for each of them not the traditional or neoclassical account of such recent physiological writers as Fernel or Riolan but mechanistic details by which the particular function is performed automatically in the homme. Each of Descartes's explanations borrows something from traditionalist physiological theories, but in each case Descartes wields Ockham's razor to strip away excess souls, faculties, forces, and innate heats from the corpuscular or chemical core of explanation.

Digestion, for example, is for Descartes only a fermentative process in which the particles of food are broken apart and set into agitation by fluids contained in the stomach. Chyle and excremental particles are then separated from one another in a filtration performed merely by a sievelike configuration of the pores and vascular openings in the intestines. Chyle particles go through another filtration and fermentation in the liver, where they thereby—and only thereby—acquire the properties of blood. Blood formed in the liver drips from the vena cava into the right ventricle of the heart, where the purely physical heat implanted there quickly vaporizes the sanguinary mass. The expansion of this sanguinary vapor pushes out the walls of the heart and arteries. Expansion with rarefaction is succeeded by cooling; and, as the vapor condenses, the heart and arteries return to their original size. The heart is fitted with a perfect arrangement of valves, and in addition the homme is served by a perpetual circulation of blood. (Descartes had read William Harvey's De motu cordis, as is also clear from his prior correspondence, but apparently took seriously only the part on circulatory motion rather than on cardiac action.) Cardiac and arterial pulsation is thus continually and automatically repeated throughout the life of the automaton by mechanical means, not under the control of an active diastolic faculty. And while the sanguinary particles are coursing through the vessels, certain of them separate off into special pores, which accounts for both nutrition and the sievelike production of such secretions as bile and urine.

After this mechanistic survey of general physiology, Descartes moves to the nervous system, which he