K at apparent connexion which results from the 

 astomosis of a fasciculus of fibres of the one 

 \vith a portion of the other. Secondly, the 

 removal of the portion of the nervous centre 

 with which any one of the nerves concerned 

 in the sympathetic action is connected, will 

 prevent the development of the phenomenon, 

 although the nerves themselves remain un- 



SYMPATIIY. 



855 



nerves. The limitation of the irritation to 

 one or two nerves depends on the degree of 

 the stimulus, and the absence of any move- 

 ments is due to the disposition of the phrenic 

 nerve on the surface being unfavourable for 

 the excitation of motions by irritation of its 

 peripheral branches. And the experiment 

 cited from Miiller, in the last paragraph, 



injured in their peripheral distribution, or in shows that simple irritation of the trunk of a 



",1 1 ,. 1 _ . fTM . ' 11 f* l._ _" ' ' . I .. 1 



their connexion with each other. Thirdly, if 

 there were any peripheral communication be- 

 tween nerves, it would be most likely to take 

 place in the plexuses. Experiments, how- 

 ever, upon the nerves which lead to these 

 show that each nerve-tube, in its passage 

 through them, retains its isolation as dis- 

 tinctly as in any other part of its course. 

 The three nerves which supply the lower 

 extremity in the frog, says Miiller, form a 

 plexus from which two nervous trunks issue : 

 if one of these latter be divided and isolated 

 from all its connexions with muscles, and the 

 portion of it connected with the plexus irri- 

 tated, the impression will be transmitted in 

 the centripetal direction by the sensitive fibres 

 of nerve; but the motor fibres of the other 

 nerve arising from the plexus are not affected, 



Kl excite no contractions in the muscles to 

 ch they are distributed.* 

 n applying these principles to the expla- 

 ion of the instances which we have quoted, 

 shall find it difficult to determine the cen- 

 connexion in some, although in others 

 h a connexion is highly probable. It re- 

 . jis, therefore, for future anatomical re- 

 search to ascertain what that connexion is 

 which enables one nerve to sympathise with 

 another. In the instance of pain in the 

 shoulder in sympathy with irritation of the 

 liver, the hepatic irritation excites a change 

 in some sensitive nerves, which is propagated 

 to the centre, and there affects some of the 

 sentient fibres distributed in the region of the 

 shoulder. The phrenic and the external tho- 

 racic nerves are both or either of them, but 

 more especially the former, favourably situ- 

 ated to constitute the excitant of such a 

 sympathetic sensation. The phrenic nerve 

 of the right side is largely distributed upon 

 the peritoneal surface of the diaphragm, and 

 upon the inferior vena cava, and forms many 

 connexions with the hepatic plexus in the 

 substance of the liver. It may therefore 

 readily participate in any irritation of that 

 organ. Now, the phrenic nerve is implanted 

 in the spinal cord on a level with the third or 

 fourth cervical nerves ; and the nerves of the 

 shoulder form their connexion with this cen- 

 tral organ about the same level. The origins 

 of these nerves, therefore, are sufficiently 

 contiguous to each other to warrant the be- 

 lief that an irritated state of one may be pro- 

 pagated to the other through the vesicular 

 matter of the centre. But it may be inquired 

 why the irritation is limited to sensitive 

 nerves of the shoulder ; and why movements 

 are not excited by the stimulation of the 

 motor fibres of the phrenic itself, or of other 

 * Baly's Miiller, vol. i. p. 75G. 



compound nerve in connexion with the centre 

 is not sufficient to produce motion ; which 

 requires probably either a more prolonged 

 and violent irritation of the nerve,, or a polar 

 state of the centre in which it is implanted. 



Some of the instances of sympathetic sen- 

 sations, referred to above, do not admit of an 

 explanation so obvious. The pain over the 

 brow from ice or cold water in the stomach 

 may be referred to irritation of the gastric 

 branches of the vagus, communicated in the 

 medulla oblongata to the fifth ; but why the 

 irritation should be limited to the ophthalmic 

 division of the fifth cannot be accounted for 

 in the present state of our knowledge. 



In those sympathetic movements which are 

 of ordinary and normal occurrence, two pro- 

 visions seem to be secured, namely, a certain 

 peripheral organisation of the excitor nerve,, 

 and a certain central relation between it and 

 the motor nerve. But in those which are of 

 a morbid kind, it is necessary to suppose the 

 existence of a more or less exalted polarity 

 of the centre in order to explain the pheno- 

 mena fully. This polar state will continue in 

 many instances even after the primary peri- 

 pheral irritation has been removed, as in te- 

 tanus, or in the convulsions from intestinal 

 irritation ; and we learn from this fact the 

 importance in practice of attending to the 

 state of the nervous centre, as well as to the 

 removal of the irritating cause. 



There are other sympathetic phenomena, 

 of the physical kind, in which, however, the 

 nervous system does not appear to take a 

 prominent part. Such are the changes which 

 occur in different and distant organs in con- 

 nexion with a particular period of life, or the 

 development of a particular function. Among 

 these are the phenomena of puberty in both 

 sexes ; the enlargement of the mammae in 

 pregnancy. Whatever part the nervous sys- 

 tem may take in such changes, it is impos- 

 sible to account for them by reference to that 

 system only ; they must rather be regarded 

 as phenomena of nutrition occurring in har- 

 mony with the laws of growth, and there- 

 fore affecting the vital fluid more particularly 

 than any part of the system of solid parts. 



Continuity of texture disposes, as is well 

 known, to the extension of a diseased state 

 originating at some one point. So also does 

 contiguity. Phlegmonous inflammation of the 

 areolar tissue, and erysipelas in the skin, 

 spread with great rapidity. Inflammation 

 arising in one of the opposed surfaces of a 

 serous membrane readily attacks the other. 

 These effects have been vaguely assigned to 

 sympathy (the continuous and contiguous sym- 

 pathy of Hunter). But it cannot be supposed 



3 i 4 



