310 SPECIAL PHYSIOLOGY. 



the medulla oblongata. The sympathetic nerves of the heart are con- 

 nected with the cervical and upper dorsal region, and those of the 

 intestines, with the lower dorsal portion of the cord. It is further 

 supposed, that when, from any cause, the ordinary amount of stimulus, 

 proceeding from the spinal cord to the sympathetic, is withdrawn, the 

 vessels then dilate, as in the act of blushing, and under other condi- 

 tions, contract, so as to cause pallor. But these phenomena are also 

 dependent on the relative force of the heart's action, as in passion or 

 fear. The movements of the viscera may also be affected, as shown 

 by agitation of the heart, or by increased peristaltic action of the in- 

 testines. 



Emotional movements may likewise be produced in parts supplied 

 by the sympathetic nerves, and the stimuli which produce them must 

 of course originate in the cerebrum or centre of the emotions. There 

 is reason to believe that ideas even may act in a similar manner. 



Instinctive causes, or like actions of the cerebro-spinal system, may 

 produce effects upon associated parts, which must take place through 

 the sympathetic nerves; as, for example, when the act of sucking pro- 

 duces an accompanying increase in the flow of saliva. The similar 

 increased secretion of the lachrymal gland in shedding tears, affords 

 evidence of an emotional stimulus affecting a gland through its sym- 

 pathetic nerves; and the flow of saliva, at the thought of a coming 

 meal, affords similar evidence as regards ideational stimuli. Indeed, 

 such glands as the lachrymal and salivary glands, which act only at 

 certain intervals, and are particularly affected by mental states, re- 

 ceive, besides sympathetic nerves, many branches from the cerebro- 

 spinal system. But strong mental stimuli may also arrest the lachry- 

 mal secretion, as is well seen when a person is overpowered by grief; 

 in like manner, the flow of saliva may be checked by strong emotions. 

 It is probable that the gastric secretion is, like the saliva, also excited 

 by mental stimuli; it has been seen to be rapidly secreted in fasting 

 dogs, at the sight of food. 



Of simple reflex acts, performed through the cords and ganglia of 

 the sympathetic, we have numerous instances; and in these cases, too, 

 we shall find that sometimes they are performed through the inter- 

 vention of the spinal cord ; though cases may be quoted in which the 

 sympathetic must act altogether independently of the cerebro-spinal 

 system. Thus, it is said, when the visceral nerves of the abdomen of 

 an animal are powerfully galvanized, movements of the abdominal 

 muscles are excited; and irritation of the frog's intestines or liver will 

 also excite movements in certain voluntary muscles. 



In the human subject, too, both the striated and non-striated mus- 

 cles may be affected through the sympathetic nerves, for strabismus 

 or squinting, convulsions in infants, and epileptic attacks in the adult, 

 are sometimes caused by worms, or irritating substances, in the ali- 

 mentary canal ; moreover, a form of paralysis, known as reflex paral- 

 ysis, and certain muscular symptoms, showing disturbance of the ner- 

 vous system, are sometimes induced by disease or irritation of distant 

 viscera, or of highly sensitive parts, such as the dental nerves; whilst 

 colic and even diarrhoea frequently result from the introduction of 



