Cullen was the father of modern Solidism,--a system based upon the solid parts of the body, the nerves being the chief agents. The life-giving element was, in his view, an undefined, dynamic something (different from Hoffmann's ether or Stahl's soul), which he called _nerve-force, or nerve-principle; animal force; and brain-energy_, and in it he included the spinal cord. His nerve-principle was supposed to produce spasms and atony, either actively or passively. The causes of disease, while of a debilitating character, were supposed to awaken reaction of the healing powers of Nature; fever was a reparative effort of Nature, even in its cold stage, the blood playing no part in it. He constructed a very arbitrary classification of fevers, as, in fact, he did of all diseases, his system of nosology being the secret of his reputation. His explanation of gout was famous. That disorder, he said, depended upon an atony in the digestive organs against which was periodically set up a reparative effort in form of a{190} joint inflammation. In scrofula he had to assume, in contradiction to his nervous pathology, a peculiar acridity, and in putrid fever a putridity of the humors of the body. His therapeutics were simple and salutary, because of his renunciation of venesection, which was much abused in his day. The most celebrated pupils and successors of Hoffmann were Gregory, of Edinburgh, Gardiner, and, in Germany, the famous Thaer (1752-1828), who finally abandoned the practice of medicine because it promised more than it could perform, and who became a "father of husbandry."