  According to Montesquieu, a cold climate constricts our bodies' fibers, and causes coarser juices to flow through them. Heat, by contrast, expands our fibers, and produces more rarefied juices. These physiological changes affect our characters. Those who live in cold climates are vigorous and bold, phlegmatic, frank, and not given to suspicion or cunning. They are relatively insensitive to pleasure and pain; Montesquieu writes that "you must flay a Muscovite alive to make him feel" (SL 14.2). Those who live in warm climates have stronger but less durable sensations. They are more fearful, more amorous, and more susceptible both to the temptations of pleasure and to real or imagined pain; but they are less resolute, and less capable of sustained or decisive action. The manners of those who live in temperate climates are "inconstant", since "the climate has not a quality determinate enough to fix them" (SL 14.2). These differences are not hereditary: if one moves from one sort of climate to another, one's temperament will alter accordingly.