452 SYMPATHY. 



ascribe other purposes to them any more than to those nerves of 

 the same class that do not run to ganglia. They take this course 

 probably for convenience and complete mingling ; just as the 

 spinal nerves of sense and motion run together in one trunk, and 

 these mingle by means of plexuses. 



I may remark that it is even requisite not only for different 

 organs but for different structures in the same organ to sympa- 

 thise : a stimulus applied to the inner surface of the alimentary 

 canal, heart, or urinary bladder, causes the muscular fibres to 

 contract. 



This mutual influence is sympathy ; and it exists universally 

 throughout the system, although the more palpable and striking 

 instances of it only pass usually under that name. 



We will now consider sympathy more minutely. 



By sympathy h is meant the affection of one part of the body 

 directly by the affection of another, through vital agency alone, 

 independently of physical. When the sun shines into our eyes, 

 or something irritates the nostrils, the expiratory muscles con- 

 tract violently and we sneeze by sympathy. If the fauces are 

 tickled, we vomit by sympathy. If cold is suddenly applied to 

 the surface, the bladder endeavours to expel its contents by 

 sympathy. This property of sympathising is indispensable to 

 the functions of the body. Unless the operation of one part 

 is varied according to the condition of another, the harmony 

 of our functions would be destroyed. When the uterus has been 

 gravid its full time, the breasts secrete milk : perhaps before this 

 period, or whenever it may expel its burden. The presence of 

 food in the mouth produces a flow of saliva from all the salivary 

 ducts ; and when semen touches the inner surface of the urethra 

 the levatores ani and ejaculatores seminis are thrown into con- 

 vulsions. When the skin perspires but little, the kidneys secrete 

 more urine. The extreme importance of sympathy will appear 

 when we consider that it occurs not only between different 

 organs, but different parts of the same organ. The blood, the 

 chyme, the faeces, are not applied to the muscular portions of the 

 vascular and alimentary systems, but to their lining membrane ; 



h " J. H. Rahn, De causis physicis Sympathise, Exerc. i. vii. Tigur. from 

 1786. 4to. Sylloge select, eorum opu&cul. de mirabili sympathia qua paries inter 

 diversas c. h, intercedit. Edited by J. C. Tr. Schlegel, Lips. 1787. 8vo." 



