68. Giovanni Alfonso Borelli (1608-1670) was the head of the so-called iatro-mathematical sect. He tried to apply mathematics to medicine in the same way in which it had been applied to the physical sciences. He was wise enough to restrict the application of his system to the motion of the muscles, but his followers tried to extend its application and were led into many absurd conjectures. Borelli was at first professor of mathematics at Pisa, and later professor of medicine at Florence. He was connected with the revolt of Messina and was obliged to leave Florence. He retired to Rome, where he was under the protection of Christina, Queen of Sweden, and remained there until his death in 1679. [139] 69. "For one order that the will gives, it bows a hundred times to the yoke." Descartes, on the other hand, teaches that the soul has direct control over its voluntary actions and thoughts, and indirect control over its passions. [140] La Mettrie goes further than to limit the extent of the will, and questions whether it is ever free: "The sensations which affect us decide the soul either to will or not to will, to love or to hate these sensations according to the pleasure or the pain which they cause in us. This state of the soul thus determined by its sensations is called the will." [141] Holbach insists on this point and contends that all freedom is a delusion: "[Man's] birth depends on causes entirely outside of his power; it is without his permission that he enters this system where he has a place; and without his consent that, from the moment of his birth to the day of his death, he is continually modified by causes that influence his machine in spite of his will, modify his being, and alter his conduct. Is not the least reflexion enough to prove that the solids and fluids of which the body is composed, and that the hidden mechanism that he considers independent of external causes, are perpetually under the influence of these causes, and could not act without them? Does he not see that his temperament does not depend on himself, that his passions are the necessary consequences of his temperament, that his will and his actions are determined by these same passions, and by ideas that he has not given to himself?... In a word, everything should convince man that during every moment of his life, he is but a passive instrument in the hands of necessity." [142] 70. The theory of animal spirits, held by Galen and elaborated by Descartes, is that the nerves are hollow tubes containing a volatile liquid, the animal spirits. The animal spirits were supposed to circulate from the periphery to the brain and back again, and to perform by their action all the functions of the nerves. 71. Berkeley uses the fact that the color of objects varies, as one argument for his idealistic conclusion. [143]