586 THE SYMPATHETIC SYSTEM. 



sensible phenomena obtained by experimenting on the sympathetic 

 nerves are, in many cases, slow in making their appearance, and not 

 particularly striking or characteristic in their nature. 



Notwithstanding these difficulties, however, some facts have been 

 ascertained with regard to this part of the nervous system, which give 

 a certain degree of insight into its character and functions. 



Influence on Movement and Sensibility. The sympathetic system is 

 endowed both with sensibility and the power of exciting motion ; but 

 these properties are less active than in the cerebro-spinal system, and 

 are exercised in a different manner. If we irritate a sensitive spinal 

 nerve in one of the limbs, or apply the galvanic current to its posterior 

 root, the evidences of pain or of reflex action are decisive and instanta- 

 neous. There is no appreciable interval between the application of the 

 stimulus and the sensation which results from it. On the other hand, 

 in experiments upon the sympathetic ganglia and nerves, evidences of 

 sensibility are also manifested, but much less acutely, and only after 

 somewhat prolonged application of the irritating cause. These results 

 correspond with what we know of the physiological properties of the 

 organs supplied by the sympathetic system. These organs are insen. 

 sible, or nearly so, to ordinary impressions. We are not conscious of 

 the changes going on in them, so long as the} 7 retain a normal character. 

 But they are still capable of perceiving unusual or excessive irritations, 

 and may even give rise to acute pain when in a state of inflammatory 

 alteration. 



There is the same peculiar character in the action of the motor nerves 

 belonging to the sympathetic system. If the facial or hypoglossal, or 

 the anterior root of a spinal nerve, be irritated, the convulsive movement 

 which follows is instantaneous, spasmodic, and momentary in duration. 

 But if the semilunar ganglion or its nerves be subjected to a similar 

 experiment, no immediate effect is produced. It is only after a few 

 seconds that a slow, vermicular, progressive contraction takes place in 

 the corresponding part of the intestine, which continues for some time 

 after the exciting cause has been removed. 



Morbid changes taking place in organs supplied by the sympathetic 

 present a similar peculiarity in their production. If the body be exposed 

 to cold and dampness, congestion of the kidneys shows itself perhaps on 

 the following day. Inflammation of any internal organ is rarely estab- 

 lished within twelve or twenty-four hours after the application of the 

 exciting cause. The internal processes of nutrition, together with their 

 derangements, which are more especially under the control of the sym- 

 pathetic, require a longer time to be influenced by incidental causes, 

 than those which are regulated by the cerebro-spinal system. 



Connection with the Special Senses. In the head, the sympathetic 

 has an important connection with the special senses. This is noticeable 

 more particularly in the case of the eye, in the influences regulating the 

 expansion and contraction of the pupil. The ophthalmic ganglion sends 

 off a number of ciliary nerves, distributed to the iris, and receives a 



