SYiMPATHETIC NERVE. 



455 



At least, in embryos near the full time, they 

 observed little change in the sympathetic 

 nerve-fibres. 



It has been already stated that in the sym- 

 pathetic of embryos of 18 or 19 inches in 

 length there are some tubular fibres present ; 

 these, probably, are to be regarded as fibres 

 sent from the cerebro-spinal system. 



PHYSIOLOGY. The actions which take 

 place in the animal body may be divided into 

 two classes. Those which are included in 

 the one class are entirely under the guidance 

 of volition ; those which belong to the other 

 not only take place independently of any 

 effort of the will, but are also more or less 

 completely removed beyond its control. The 

 movements which occur in the muscles of the 

 limbs, and in most of the muscles of the 

 trunk, form examples of the former ; while 

 the movements of the internal muscular 

 organs, such as those of the heart, intestinal 

 canal, and genito-urinary organs, afford ex- 

 amples of the latter. To the latter also be- 

 long the acts of nutrition, secretion, &c., 

 commonly termed the vegetative processes. 

 Several of the latter, as the movements of 

 the heart, go on without interruption during 

 the entire life of the individual; while others, 

 as the movements of the intestinal canal, take 

 place at irregular intervals, depending ap- 

 parently on the application of external stimuli 

 to the free surfaces of the organs in which 

 they are manifested. The exercise of the 

 former class of actions is moreover attended 

 by sensation ; that of the latter, in the normal 

 condition, not. The impressions which are 

 constantly being made by the blood upon the 

 inner surface of the heart and vessels never 

 reach the sensorium ; we are also insensible 

 to the impressions made by the food upon the 

 free surface of the intestinal canal, as well as to 

 the contractions thereby induced. In like 

 manner, the acts of nutrition and secretion take 

 place entirely without our knowledge. The 

 feeling of weariness also which ensues after 

 exertion of the voluntary muscles, is never 

 felt so far as the heart is concerned, although 

 its action is constant, and just as little in re- 

 gard to the other organic muscles. 



The organs in which the former class of 

 actions takes place are supplied with nerves 

 which proceed directly from the brain and 

 spinal cord ; those whose actions belong to 

 the second class derive their nerves chiefly 

 from the sympathetic. 



Guided by this difference in character be- 

 tween the vital phenomena, Bichat divided 

 life into animal and vegetative ; the former 

 characterised by the circumstance of its 

 phenomena coming within the range of sen- 

 sation and volition ; the latter including those 

 acts which are more or less completely re- 

 moved beyond the sphere of the will and 

 of the consciousness. In accordance with 

 this division, he also separated the nervous 

 system into two portions : the one corre- 

 sponding to the cerebro-spinal system, pre- 

 siding over the functions of animal life ; the 

 other corresponding to the sympathetic, pre- 



siding over the involuntary movements, and 

 over the processes of nutrition and secretion, 

 or functions of vegetative life. The sympa- 

 thetic and its ganglia are, according to the 

 views of Bichat, entirely independent of the 

 cerebro-spinal system of nerves. The various 

 ganglia of the sympathetic he regarded as so 

 many distinct nervous centres, each presiding 

 over the actions of the parts to which it sends 

 nerve-filaments, and each discharging its func- 

 tions without any relation to the brain or the 

 spinal cord. The involuntary nature of the 

 processes which take place in organs supplied 

 by the sympathetic, as well as the circum- 

 stance that the normal impressions which are 

 made upon the free surfaces of these do not 

 reach the sensorium, rendered the views of 

 Bichat highly probable. In diseases of the 

 brain and spinal cord, as in tetanus and 

 chorea, where the muscles supplied by cerebro- 

 spinal nerves are all thrown into a state of 

 more or less violent contraction, the muscular 

 organs which derive their nerves from the 

 sympathetic, such as the heart, continue their 

 movements as before. So also a stimulus ap- 

 plied to the brain or spinal cord, causes con- 

 tractions in the muscles which derive their 

 nerves from these parts, but does not, ac- 

 cording to Bichat, produce any effect on the 

 movements of parts which are supplied by 

 the sympathetic. The fact that embryos in 

 which the central masses of the nervous 

 system are wanting may reach an advanced 

 stage of development, showed that the pro- 

 cesses of vegetative life might go on perfectly, 

 independently of the influence of the cere- 

 bro-spinal system, while the circumstance that 

 in these the sympathetic system of nerves was 

 always present, and in a high state of develop- 

 ment, seemed at the same time to indicate 

 the connection subsisting between it and the 

 processes in question. 



The views of Bichat were generally adopted 

 by physiologists until comparatively recent 

 times, when they were ably combated by 

 Valentin, who endeavoured to establish the 

 doctrine, commonly held before the time of 

 Bichat, that the sympathetic and cerebro- 

 spinal nerves do not constitute two distinct 

 and independent systems, but that the former 

 is dependent upon the latter for all its pro- 

 perties, and is in this respect to be regarded 

 as one of the cerebro-spinal nerves. The in- 

 voluntary and apparently spontaneous nature 

 of the movements which take place in organs 

 supplied by branches of the sympathetic, 

 affords no argument, according to Valentin, 

 for supposing that their action is not regu- 

 lated by the brain and spinal cord, or that 

 the sympathetic is independent of these parts 

 of the nervous system, inasmuch as the same 

 character is also presented by the movements 

 of certain] organs which are undoubtedly 

 supplied by cerebro-spinal nerves. This, for 

 example, is the case with the rhythmical 

 movements of the muscles of respiration. 

 Again, there are organs which are supplied by 

 nerves of cerebro-spinal origin, and which 

 notwithstanding resemble the organs supplied 



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