Some of the most noted leaders of thought in our own era were likewise chronic invalids. Among these were the scholarly theologian, E. B. Pusey, and J. A. Symonds, the historian of the Renaissance. There was also Herbert Spencer, who was frequently forced by nervous breakdowns to take long periods of absolute rest. More remarkable still was the case of the famous naturalist, Charles Darwin. "It is," writes his son, "a principal feature of his life that for nearly forty years he never knew one day of the health of ordinary men, and that thus his life was one long struggle against the weariness and the strain of sickness."[94] But, notwithstanding his continued ill health and the spinal anemia from which he suffered, he was able to conduct those epoch-making researches which put him in the forefront of men of science, and to write those famous books which have completely revolutionized our views of nature and nature's laws. But a still more remarkable illustration of the fact that there is no necessary relation between muscular and mental power, between physical well-being and intellectual energy, is afforded by the illustrious discoverer of the world of the infinitely little, Louis Pasteur. Stricken by hemiplegia shortly after he had begun those brilliant investigations which have rendered him immortal, he remained affected by partial paralysis until the end of his life. His friends had reason to fear that this attack, even if he should survive it, would weaken or extinguish his spirit of initiative, if it did not make further work entirely impossible. But this was far from the case. For a quarter of a century he continued with unabated activity those marvelous labors which are forever associated with his name. And it was after, not before, his misfortune that he made his most famous discoveries in the domain of microbian life, and placed in the hands of physicians and surgeons those infallible means of combatting disease which have made him one of the greatest benefactors of suffering humanity. The complete separation of the intellectual from the motor faculties was never more clearly exhibited than in this case, nor was it ever more completely demonstrated by an experiment, whose validity no one could question, that power of mind does not necessarily depend on strength or health of body. It proved, also, in the most telling manner that it is not muscular but psychic force which avails most, whether to the individual or to society. And it showed, at the same time, the utter absurdity of those theories which would fatally connect intellectual with physical debility in woman, and would forever adjudge the physically weaker sex to be of hopeless inferiority in all things of the mind.