NERVOUS SYSTEM. 



NETTLE. 



SO 



become capable of forming his own character, and therefore truly 

 responsible for his actions. It must not be forgotten however, that 

 the power of salf-control may be turned to a bad as well as to a good 

 account ; and that the value of its results will entirely depend upon 

 the direction in which it is employed. The thoughts may be so deter- 

 minatively drawn away from the higher class of motives, the suggestions 

 of conscience so habitually disregarded, and the whole attention so 

 completely fixed upon the gratification of selfish or malevolent pro- 

 pensities, that the human nature acquires far more of the Satanic 

 than of the Divine character ; the highest development of this type 

 (if the term may be permitted) being displayed by those who use 

 their power of self-control for the purposes of hypocrisy and dis- 

 simulation, and cover the most malignant designs under the veil of 

 friendship. 



" Such men (whose portraiture is presented by our great dramatist 

 in the character of lago) show us to what evil account the highest 

 intellect and the most powerful will may bo turned when directed by 

 the baser class of motives ; and we cannot but feel that they are far 

 more degraded in the moral scale than those who, having never learned 

 to control their animal propensities, and being unconscious of the 

 very existence of a higher nature within themselves, simply obey the 

 promptings of their automatic impulses, and are rather to be con- 

 sidered an ill-conditioned automata than as vicious men. Of this latter 

 class, some, from original constitution and early influences of the most 

 degrading kind, seein altogether destitute of anything but a brutal 

 nature ; such ought to be treated as irresponsible beings, and as such 

 restraiued by external coercion from doing injury to society. But this 

 clas.-i is small in proportion to that of individuals who act viciously 

 simply because they have never been led to know that any other cours* 

 is open to them, or to feel any motive that might give them a different 

 impulse. With these the object should rather be to awaken the higher 

 parts of the moral nature, ' to find out the holy spot in every child's 

 heart,' and to develop habits of self-control in the manner just 

 described, than to subjugate by external restraint ; and the success 

 which has attended this method, in the hands of those who have 

 judiciously applied it, is sufficient evidence of its superiority ; many of 

 the most apparently-debased natures having been thus elevated to a 

 grade which it seemed at first impossible they could ever attain. 

 From the Satanic or positively and wilfully evil type of human nature, 

 in which the highest powers are turned to the worst account, we are 

 thus conducted through the brutal or negatively evil type, towards 

 that higher aspect of humanity which is presented by those who 

 habitually keep before them the Divine ideal, and who steadily endea- 

 vour to brine,- their whole nature into conformity with it. This is not 

 to be effected by dwelling exclusively on any one set of the motives 

 already referred to, as those which the truly religious man keeps before 

 hix mind. Even the idea of duty, operating alone, tends to reduce the 

 individual to the subservience of a slave, rather than to induce in him 

 that true mastery over himself which consists in such a regulation of 

 his emotions and propensities, that his course of duty becomes the 

 spontaneous expression of his own higher nature ; but it is a most 

 powerful aid in the acquirement of that regulation, by the fixation 

 of the thoughts and affections on ' things on high,' which is the best 

 means of detaching them from all that is earthly and debasing. It is 

 by the assimilation, rather than by the subjugation, of the human will 

 to the divine that man is really lifted towards Qod ; and in proportion 

 as this assimilation has been effected, does it manifest itself in the life 

 and conduct ; so that even the lowliest actions become holy ministra- 

 tions in a temple consecrated by the felt presence of the Divinity. Such 

 was the life of the Saviour; towards that standard it is for the Christian 

 disciple to aspire." (Carpenter, ' Human Physiology,' page 84S.) 



In the previous view of the Nervous System we have not spoken of 

 the Sympathetic Nerve. 



The system of the great Sympathetic Nerve is that whose branches 

 are distributed to all the organs of organic life, the heart, lungs, 

 digestive canal, and glands, &c., chiefly following the course of the 

 blood-vessels, bearing numerous and large ganglia in all parts of their 

 course, and communicating with the brain and spinal chord or their 

 nerves only by few and small filaments. The parts to which the 

 branches of the sympathetic nerve are distributed have but vague if 

 any sensibility, unless under peculiar circumstances of disease ; and 

 ' the motions which some of them possess are usually quite independent 

 of the mind. Numerous experiments of irritating the ganglia of the 

 sympathetic to see whether it produces pain, have had unsatisfactory 

 results ; nor would any results of apparent insensibility be conclusive, 

 because the ganglia might, like part of the brain, be insensible to 

 injury, though fully capable of perceiving the. impressions transmitted 

 to them through their nerves. But the pain of the diseases of internal 

 organs is amply sufficient to prove their sensibility, though it does 

 tennine whether the impression of pain is conveyed through 

 filaments of the sympathetic system or through those few of the 

 eerel<ro-spinal nystrrn which are mingled with the former in the common 

 sheath. In the same manner, in extraordinary cases, the brain nnd 

 ! chord have an evident influence on the motions of the organs 

 supplied by the sympathetic nerve, as in the effects of strong passion 

 and other mental affections on the circulation, the digestive functions, 

 &o. The impressions conveyed from the viscera to the brain and 

 spinal chord may also be ret! 'ted either to the voluntary muscles, as 



in the convulsions of children with disordered digestion, or to the 

 involuntary muscles, as in the increased rapidity of pulse, the sickness, 

 &c., which occur in various diseases. 



In the natural state however, the organs chiefly supplied by the 

 sympathetic nerves are entirely independent of the cerebro-spiual 

 system, and will maintain their actions for a time even after their 

 removal from the body. Thus the peristaltic motion of the intestines, 

 the contractions and dilatations of the heart of some animals, and 

 some other similar actions, will continue for a considerable time after 

 they are separated from the body, or after all the nerves passing to 

 them have been divided. Many other facts prove also that the internal 

 organs are much less dependent on the influence of the sympathetic 

 nerve than the external animal organs are on that of their cerebro- 

 spinal nerves : severe irritation of the sympathetic nerves, such as, 

 if applied to the cerebro-spinal motor nerves, would excite sudden 

 and violent convulsions of their muscles, gives rise to but weak and 

 slow contractions of the viscera ; and these follow at perceptible 

 intervals after the application of the stimulus, so that it is often 

 difficult to say whether the irritation has exerted any influence at all. 



The office of the numerous ganglia placed in the course of the 

 sympathetic nerves is perhaps the most obscure point in the whole 

 range of physiology. Some have regarded them as so many brains, 

 by which impressions are received through the branches of which each 

 ganglion is the centre, and from which excitements to motion are sent 

 out ; others have believed that they exercise a power of isolating the 

 organs they supply from the influence of the mind or of obstructing 

 the constant passage of impressions to aud from the brain ; and many 

 other functions have been supposed to be performed by them ; but 

 for each and all the evidence is altogether unsatisfactory. 



The Sympathetic Nerve, or system of nerves, has received its name 

 from the idea that it is of ultimate importance in the phenomena of 

 what is called sympathy, in which one part of the body is affected in 

 consequence of some peculiar condition of another. A great number 

 of the phenomena which were formerly regarded as the effects of 

 sympathy are now more clearly explained by the reflecting action of 

 the cerebro-spinal axis; many others depend on some generally 

 operating influence, as a peculiar condition of the blood, &c. ; aud in 

 those that remain it is questionable whether the sympathetic system 

 of nerveg exercises any peculiar power. The universality of its dis- 

 tribution among the viscera is the only ground on which it can be 

 believed , to possess this property of exciting impressions or actions 

 iu one, in consequence of being itself excited by the condition of 

 another. 



It exerts a more evident influence iu the various secretions of the 

 glands and other surfaces which it supplies. In some instances the 

 excitant to secretion is conveyed primarily from the brain, either 

 directly, as in the flowing of tears in grief, &c., or by a reflex action, 

 as in the tears that flow when the mucous membrane of the nose is 

 irritated, or as in the flow of saliva in a strong irritation of the mem- 

 brane of the mouth, in the sweating of fear or of great agony, Ac. 

 In the more constant secretions the influence of the sympathetic 

 nerves is iu some degree assumed ; but there are sufficient facts to 

 prove that their inj ury is very soou followed by a suppression or modi- 

 fication of the secretion in the organ to which the injured nerves are 

 destined. The cerebro-spinal nerves also exercise an influence on thf 

 secretion and nutrition of the parts which they supply; but its 

 amount is indistiuot, in consequence of the interruption of other 

 circumstances favourable to those processes, by the same injury which 

 cuts off the secretory power of the nerves, as the loss of exercise of 

 the muscles, &c. 



(The literature upon the Nervous System is very extensive. In the 

 preceding- article we have almost exclusively consulted the works of 

 Dr. Carpenter, whose several physiological works contain by far the 

 best account of the physiology of the Nervous System with which we 

 are acquainted. The following are the works of Dr. Carpenter which 

 have been consulted and used in this article : ' Principles of Human 

 Physiology,' 4th edition, 1 853 ; ' Principles of Comparative Physiology," 

 4th edition, 1854; 'Principles of Physiology, General and Compara- 

 rative,' 3rd edition, 1851; 'Manual of Physiology,' 1846. The best 

 account of the Histology of the Nervous System will be found in 

 Kolliker's ' Manual of Human Histology,' translated for the Sydeuham 

 Society by Messrs. Busk and Huxley. The following works may also 

 be consulted with great advautage on both the structure and functions 

 of the Nervous System : Valentin, ' Text-Book of Physiology,' 

 translated by Brinton ; Miiller, ' Physiology,' translated by Baly ; 

 Marshall Hall, ' Memoirs on the Nervous System ;' Newport, article 

 ' Insecta,' in ' Cyclopaxlia of Anatomy ; ' Noble, ' On the Brain ; ' 

 Todd, ' Anatomy of the Brain and Spinal Cord ; ' Kirks and Paget, 

 'Handbook of Physiology;' Unzer and Proohaska, ' On the Nervous 

 System,' translated by Luycock for the Sydeuham Society.) 



NKUVOUS TISSUE. [NEHVOUB SYSTEM.] 



NE'SEA (Lamouroux), a genus of Corallines. 



NESOTHAGUS. [ANxaoi'E.E.] 



NETTLE, a name applied to various plants. The true Nettles are 

 various species of the genus Urtica, well known for their stinging 

 properties, which are owing to the presence of an acrid poisonous 

 secretion that in some Indian species is so dangerous as to cause 

 excruciating paiu aud even death. Dead-Netties are species of Lamimn , 



