All inert bodies show no communication in their different parts. Though the extremity of a stone, or of a metal, may be altered in any way by chemical dissolution, or by mechanical agents, the other parts are not affected; it is necessary to touch them by a direct action. On the contrary, every thing is so connected and tied together in the living body, that no one part can be disordered in its functions, without being immediately perceived by the rest. All physicians have known the singular consent that exists between our different organs, both in a state of health and disease, but principally in the latter. How easy would be the study of diseases, if they were stripped of every thing derived from sympathy! Who does not know that these complaints often predominate over those that arise from the injury of the diseased organ? Who does not know that the cause of sleep, of exhalation, of absorption, of secretion, of vomiting, of diarrhœa, of retention of urine, of convulsions, &c. is oftentimes very far from the brain, from the exhalants, from the absorbents, from the glands, from the stomach, from the intestines, from the bladder, from the voluntary muscles, &c.? How little soever we reflect on the sympathetic phenomena, it will be evident that they are only unnatural developments of vital forces which are called into action in an organ by the influence that it receives from those that have been directly excited. In this view all the systems are dependant upon each other. This important point of doctrine will be treated at so much length, in this work, particularly under the article on the nervous system that it is useless to insist much upon it here. We shall see sympathies call into action always those vital properties especially that prevail in a system; animal sensibility in the nerves, contractility of the same kind in the voluntary muscles, insensible organic contractility in the involuntary, sensible contractility in the glands, in the serous, mucous, synovial, cutaneous surfaces, &c. We shall see them assume the character of the vital properties of the organs in which they are developed, their progress will be chronic in the bones, cartilages, &c. acute in the muscles, skin, &c. We shall see them observe in the frequency of their development, the laws of nutrition and growth, to appear oftener in the nervous and vascular system of the child, in the pulmonary organs in youth, and in the abdominal contents in adult age. But let us pass to other subjects. IV. _Of the vital properties and their phenomena, considered in relation to the solids and fluids._