NERVA NERVOUS DISEASES. 



175 



character and government of Nero, has not come 

 down to us. 



NERVA, the successor of Domitian, and one of 

 the most virtuous of the Roman emperors. In early 

 life, he held the consulship, and was a man of a cul- 

 tivated mind, and not without poetical talent, but 

 was advanced in age when he ascended the throne, 

 A. D. 96. He, nevertheless, performed many bene- 

 ficent acts, provided for the public tranquillity and 

 the execution of justice, and relieved the poor. Not- 

 withstanding this, there were many unfriendly to 

 him, particularly the soldiers of the guard, and there 

 was even a conspiracy formed against him. He died 

 A. D. 98. Trajan was his successor. 



NERVES. The nerves of the animal frame are 

 composed of bundles of white parallel medullary 

 threads. Every bundle is surrounded with a soft 

 sheath full of blood- vessels, and whose finest branches 

 terminate in the substance of the nerves. These 

 nerves are spread through the whole animal frame, 

 and variously connected with each other. Only the 

 epidermis, the hair, and nails are destitute of them. 

 '1 hey are of various size, according as they are com- 

 posed of more or fewer bundles of medullary threads. 

 In the course of the nerves there are a number of 

 knots ; these are called ganglions ; they are commonly 

 of an oblong shape and of a grayish colour, somewhat 

 inclining to red, which is perhaps owing to their being 

 extremely vascular. In particular parts of the body, 

 the nerves come in contact with each other, and the 

 bundles composing them are mutually interwoven to 

 such a degree that they cannot be disjoined without 

 violence. These communications are called plexuses, 

 and are found particularly in the abdomen behind the 

 stomach, and in the region of the pit of the stomach, 

 near the liver, mesentery, heart, &c. The final ter- 

 minations of the nerves are various, particularly those 

 which run to the organs of sense. In the auricular 

 organ, for instance, the nerves terminate in a soft 

 mass like pap, surrounded with moisture ; the optic 

 nerve terminates in a medullary skin ; the nerves of 

 taste terminate in little papilla: ; those of feeling in 

 the points of the fingers, and the surface of the skin 

 in general ; those belonging to the muscles are lost 

 in the texture of the same, so that their terminations 

 Ciimiot be accurately ascertained. All the nerves are 

 embraced under the general head of the nervous sys- 

 tem. This is most intimately connected with the 

 brain and the spinal marrow, which may be regarded 

 as a prolongation of it. The brain is the centre, 

 from which or to which proceed all impressions com- 

 municated to the nerves. The substance of the 

 nerves is the same medullary matter which consti- 

 tutes the brain, resembling the white of an egg, and 

 appearing, to the unassisted eye, as if composed of 

 little balls. The central termination of all the 

 nerves is in the brain and spinal marrow, where they 

 branch out into the skin or the interior of the organs. 

 The various isolated, and, in part, heterogeneous 

 structures of which the body consists, which are 

 mechanically joined by the cellular tissue, the mem- 

 branes, and the ligaments, are united into one har- 

 monious whole by means of the nerves. The vascu- 

 lar system connects them only so far as it furnishes 

 the supply of blood required for their support and 

 their operations ; but it is properly the nervous sys- 

 tem which imparts to all their life, governs their 

 operations, and establishes their sympathy and mut- 

 ual action. This is effected by means of that portion 

 of the nervous system which is diffused through the 

 abdomen, forming many nets and plexuses, and con- 

 stituting what is called the vegetative, or reproduc- 

 tive, or organic nervous system, because the growth 

 and support of the body are effected by it. Another 

 part of the nervous system affords the means of con- 



sciousness and voluntary action. This is the brain 

 or cerebral system (see these two articles), which 

 excites the nerves that put in action the muscles of 

 voluntary motion, and those which supply sensibility 

 to the organs of sense, and convey to the brain the 

 impressions thence received. The nerves which 

 communicate with the organs of sense, run in pairs 

 the first pair (olfactory nerve) to the nose, where it 

 is spread over the surface of the nostrils, and forms 

 the power of smell ; the second (optic nerve) to the 

 eyes ; this is round, thick, and penetrates from behind 

 the ball or globe of the eye (through a round plate of 

 the firm coat of the ball, containing many little aper- 

 tures) , and is spread out on the inner and concave 

 surface of the globe into a thin coat called the retina, 

 on which the images of external objects are formed ; 

 the eighth pair (auditory nerves) are spread over the 

 interior of the ear, and are sensible to the vibrations 

 of the air. From the numerous ramifications of the 

 ninth pair come the nerves of the tongue, which give 

 rise to the sense of taste. The general sense of 

 feeling is situated particularly in the skin ; and pecu- 

 liarly in the points of the fingers. This sense is pro- 

 duced by a variety of nerves diffused over the skin, 

 and those parts which are most sensitive are sup- 

 plied with the greatest quantity of nerves, which 

 form entire series of contiguous nervous papillae ; for 

 instance, at the lips, the points of the fingers, &c. 

 Thus the action of the nerves is reciprocal from with- 

 out inwards, and from within outwards the first, 

 because the impressions on the organs of sense are 

 communicated by the nerves to the brain, and there 

 form perceptions and feelings ; the second, because 

 the voluntary motions are produced by communica- 

 tions from the brain to the nerves, while the repro- 

 ductive part of the nervous system quietly supports 

 the whole machine, and, in a sound state of the body, 

 is recognised only by the operation of the appetites, 

 and by a general feeling of ease throughout the sys- 

 tem; but, in a diseased state, gives rise to general 

 uneasiness and pain. The power of the nervous sys- 

 tem has no fixed point, but is variable, even in the 

 same subject. In sleep, the activity of the cerebral 

 system is impaired, that of the reproductive system 

 heightened ; therefore, in quiet sleep, the operations 

 of the senses and the voluntary motions cease, while 

 the activity of the organs of respiration and circula- 

 tion, of digestion, secretion, and nourishment con- 

 tinues. From what has been said, it appears that the 

 whole action of the body depends upon the nervous 

 system. See Nervous Diseases. 



NERVOUS DISEASES (neuroses') are such as 

 consist in disturbed affections of sense and motion, 

 unattended by any chronic or acute inflammation, or 

 hemorrhage, or by any disturbance of the circulation. 

 Nervous pains are called neuralgias ; spasms are invol- 

 untary contractions in organs whicli have muscular 

 fibres, or which are merely susceptible of contrac- 

 tion ; convulsions are involuntary and irregular con- 

 tractions, alternating with relaxations, in one, or 

 several, or all of the muscles, simultaneously or suc- 

 cessively ; tetanus is a permanent contraction of a 

 certain class of muscles, ordinarily followed by death; 

 contraction is a retraction of the flexor muscles of one 

 member or of two parallel members ; par a ly sit is the 

 diminution or loss of the sensibility of an organ 

 of sense, or the contractility of an organ of motion. 

 The pains, spasms, paralysis, take different names, 

 according to the parts affected. The most remark- 

 able of all the neuroses is apoplexy (q. v.), which is 

 characterized by the suspension or successive loss of 

 sense and understanding, as well as of motion. The 

 affections of the mind, known under the names of 

 mental alienation, insanity, idiocy, &c., are also 

 neuroses ; that is, disturbances in the action of the 



