Before we dismiss the consideration of medical theories, however, it will still be necessary to give some account of the new system as it hath branched out in various ways: for though the fundamental principle is now received by a great number of physicians, yet the superstructure is exceedingly different from what Dr. Brown himself erected and, indeed, from the very same principles we find conclusions made as directly opposite to one another as can be expressed in words. Drs. Yates and McLean, for instance, at Calcutta in the East Indies, have concluded that the plague “is a disease of a very high degree of exhaustion;” which Dr. Brown would have called debility. Dr. Rush at Philadelphia, proceeding also upon the Brunonian principles, determines it to be the most inflammatory of all diseases,[62] and which Dr. Brown would have called a disease of excitement. These two doctrines are, in every sense of the word, as distant from one another as east from west. Let us then consider both, if any consideration can avail us on the subject. [62] See above, p. 102. By the ancients it was supposed that diseases were occasioned by something either bred in the body or received into it, and that the power of nature produced, during the course of the disease, a certain change in this matter, called _coction_, or _concoction_; which, if we please, we may express by the English word _cooking_. The matter of the disease, called also _morbific_ matter, thus _cooked_, was in a state proper for expulsion, and was therefore thrown out by sweat, vomit, stool, &c. or it might be expelled artificially, which could not have been attempted with safety before. Modern systems deny the existence of morbific matter, and resolve all into an affection of the nerves, according to Dr. Cullen by certain sedative causes, but according to Dr. Brown by an accumulation in some cases, and an exhaustion in others, of the excitability or excitement of the body. The Science of Life commences with stating what they suppose to be an improvement of the Brunonian principles, and from which the following account of the origin of diseases is extracted. “Upon the different states of _excitability_ depend all the phenomena of health and disease. There are three states of the excitability. 1. The state of accumulation; when a portion of the usual stimuli is withheld.... When a portion of the usual stimuli is withheld, the excitability accumulates, and the body becomes susceptible of impression in the direct ratio of the subduction. This state constitutes diseases of accumulation, or of direct debility. 2. The middle state; when the excitability is such that the application of the accustomed degree of exciting powers produces _tone_ or _health_. 3. The state of exhaustion. When the application of stimuli has been greater than that which produces healthy action, the excitability is exhausted, and the body becomes less susceptible of impression in the direct ratio of the excess. This