SYSTEM OF THE GREAT SYMPATHETIC. 521 



The membrane of the tympanum, accordingly, which is an elastic 

 sheet, stretched across the passage to the internal ear, may be made 

 more or less sensitive to sonorous impressions by varying its con- 

 dition of tension or relaxation. This condition is regulated, as we 

 have already seen, by the combined action of the two muscles of 

 the middle ear, viz., the tensor tympani and the stapedius. The 

 first named muscle, the action of which is perfectly well understood, 

 is supplied with nervous filaments from the otic ganglion of the 

 sympathetic. By its contraction, the handle of the malleus is drawn 

 inward, bringing the membrana tympani with it, and putting this 

 membrane upon the stretch. On the relaxation of the muscle, the 

 chain of bones returns to its ordinary position, by the elasticity of 

 the neighboring parts, and the previous condition of the tympanic 

 membrane is restored. This action, so far as we can judge, is purely 

 involuntary. But the stapedius muscle is separately supplied by a 

 minute branch of the facial nerve. It is probable that this arrange- 

 ment enables us to make also a certain degree of voluntary exer- 

 tion, in listening intently for faint or distant sounds. 



In all these instances, the reflex action taking place in the 

 deeper seated muscles, originates from a sensation which is con- 

 veyed inward to the cerebro-spinal centres, and is then transmitted 

 outward to its final destination through the medium of one of the 

 sympathetic ganglia. 



Another very striking fact, concerning the sympathetic, relates to 

 the changes produced by its division, in the nutritive processes of 

 the parts supplied by it. One of the most important and remark- 

 able of these changes is an elevation of temperature in the affected 

 parts. If the sympathetic nerve be divided on one side of the neck, 

 in the rabbit, cat, or dog, an elevation of temperature begins to be 

 perceptible on the corresponding side of the head in a very short 

 time. In the cat, we have found a very sensible difference in 

 temperature between the two sides at the end of ten minutes : 

 and in the rabbit, at the end of half an hour. A vascular conges- 

 tion of the parts also takes place, which may be seen to great 

 advantage in the ear of the rabbit, when held up between the eye 

 and the light. The elevation of temperature, in these cases, is very 

 perceptible to the touch, and may also be measured by the thermo- 

 meter. Bernard 1 has found it to reach 8 or 9 F. The elevation 

 of temperature and congested state of the parts are sometimes found 

 to be diminished by the next day, and afterward disappear rapidly. 



1 Recherches Experimentales sur le Grand Sympathique. Paris, 1854. 



