The body is exhausted by too great an evacuation; hence arises weakness, an extraordinary tenuity of the humours, and, what it is generally productive of, a diseased mobility. Suppose the blood were to run copiously from a wound, or the gastric fluids were to be pour’d forth by the anus, or the breasts suck’d too long, or a greater discharge of saliva made by spitting, or the wretched body were to be troubled with a long diabetes, or in short, any other evacuations were too much increased, the strength would decline, and the health be lost; but whilst the nerves act, their fluid runs out of the body, and carries off the strength with it; nor is there any thing in the body either more labour’d, more necessary in many animal functions, or more intimately connected with strength. In studious men, therefore, a perpetual dissipation of the nervous fluid springs from the incessant action of the nerves, attended with weakness, and an extraordinary mobility, from whence all the above-mention’d diseases easily take rise; these are very dreadful, but diseases still more dreadful remain to be describ’d. It is not easy for the mind not to throw out at will such motions as it has powerfully conceiv’d; and this is a second cause of the diseases of studious men, from whence spring so many errors and wanderings of the mind, to be chang’d for death only, so many phrenzies and deliriums: for whilst ideas no longer answer to their external objects, but to the internal disposition of the brain, the latter being agitated by its own motion, either entirely, or in part, is unable to receive new vibrations, to be transmitted, all, or some, by the senses; whereas those that are spontaneous cannot be check’d.