The sensory organs provoke the movement of fluids in the nerves that can directly animate the muscles. This is the way Descartes explains the activity of the reflexes, or the habits that make a body move without the intervention of thoughts. Instincts,25 like hunger and thirst, are also mechanisms that arise from the body and make the fluids move toward the muscles and the soul.
The Connections between the Soul and the Body
1. The soul is jointlyâ linked to all the parts of the body via the mechanisms that regulate the assembling of organsâ (Descartes, 1649, Passions of the Soul, 1.30). He specifies that there is no spatial connection between the body and the soul, probably to dispel the theoretical tradition that professes that each part of the body corresponds to a property of the soul.
2. The cerebral nerves have a privileged connection to the soul. In reading The Passions of the Soul, I sometimes have the impression that the cavities in the brain are grottos in sea cliffs in which the tides exercise more or less strong fluctuations at the convenience of bodily events. These fluctuations also influence the soul.
3. Finally, there is the famous H gland. This gland would have a particularly important blood pathway, and therefore would be the power station that transforms the blood into nerve impulses. Suspended in a void, it can be moved from the inside by the soul or from the outside by the fluids of the body. Descartes uses this theoretical gadgetâ with the same enthusiasm as a child who learns to use a joystick to play a video game, or a person who enjoys changing the speed of a race car.