ignorance leads to rashness and crudity in practice, while ripe knowledge conduces to success, or, at any rate, to çaution in prognosis and expectancy in treatment. "Of the three diagnostic questions - Is there disease? Where is the disease? What is the disease?-the second is the one which forms the key note of these lectures. Where is the lesion producing the disordered actions or symptoms? The method to be followed in arriving at the solution of this question varies somewhat in different departments of medicine. Some lesions can be seen by the trained unaided eye, or felt by the skilled hand; the seat of others can be determined by auscultation and percussion, by the aid of instruments, such as the ophthalmoscope, laryngoscope, speculum, etc. But, in the study of the nervous system, greater difficulties are met with; we are, to a great extent, deprived of these physical aids; we can not appreciate the condition of the brain and spinal cord directly by our special senses, but only by a proper interpretation of the way in which the functions of these parts are performed. In other words, the diagnosis must be made chiefly by reasoning." To the words above quoted, I can add nothing, save an earnest endeavor to so place the subject-matter before you as to render it within the grasp of your full comprehension, provided you, in turn, earnestly seek to master it. THE BRAIN. IN man and the vertebrates, the cerebro-spinal axis may be divided into three separate portions, each perfectly independent of one another, and yet very intimately connected. These are enumerated by Meynert as follows: 1. THE CEREBRUM. 2. THE CEREBELLUM, AND THE APPARATUSES OF CERE BELLAR INNERVATION CONNECTED WITH IT. ITS 3. THE MEDULLARY PORTION OF THE SPINAL CORD, AND EXPANSIONS TO THE DIFFERENT PARTS OF THE EN CEPHALON. The nervous system of all animals may be subdivided into two distinct histological elements, nerve-cells and nervefibers. The former may be compared to the battery-cells of an electric circuit; the latter to the wires which conduct the current generated in the batteries. The nerve-cells are the chief histological elements of the so-called "gray matter" of the brain and spinal cord, and of ganglia found in other parts; while the white substance of the cerebro-spinal axis may be subdivided by the microscope into distinct fibers, which serve to connect the nerve-cells of some particular region with other nerve-cells or with the muscular apparatus. Nervous impulses may be divided into two classes: centripetal or sensory, and centrifugal or motor. The former travel from the peripheral portions of the body toward the nerve-centers; while the latter cause the muscular apparatus of the body to act, either in direct response to a sensory impression received from without (reflex movements), or as the result of volition. Microscopical research enables us to state positively that both of these two forms of nervous impulses are conducted partly through direct tracts of nerve-fibers, and partly by the intercommunication established between nerve-fibers and nerve-cells, and nerve-cells with each other. We may infer, therefore, that nerve-cells as well as nervefibers serve to maintain isolated conduction of nerve impulses; and that the former also generate and in some instances record them (cells of memory). We find the morphological expression of the first statement in the fact that the nerve-cells lie with their long axis stretched in the direction of the nervefibers with which they are connected; while the second and third propositions are established by physiological research respecting the functions of different regions of the cerebral cortex, as well as by the general arrangement of the cell ele We are forced, moreover, to accord to the nerve-cell the functional attribute of sensibility, as well as the power of generation and storage of nerve-force, and the discharge of this unknown power in the form of motor impulses. There is sufficient ground at present to warrant the belief that all centripetal- and centrifugal-conducting nerve-tracts are prolonged (in spite of apparent dismemberments and reduplications to which the white substance of the cerebrospinal system is subjected in passing through different collections of gray matter scattered along their course) to the most distant centers of the nervous mechanism, and find a direct and intimate connection with the nerve-cells of the gray substance of the cerebral convolutions. It seems but rational to assume that the phenomena of consciousness, which spring purely from the confluence and union of the various processes of perception, have their seat in the activity of the cerebral lobes; to which all the centripetal or sensory tracts converge and from which all the centrifugal or motor tracts arise. |