26 OF THE VITAL POWERS. 



The primary and most extensive cause of sympathy 

 must be referred to the nerves,* and indeed chiefly to 

 the serisorial reaction ;*\- so that if one nervous portion 

 is excited, the sensorium is affected, which, reacting by 

 means of the nerves on another part, draws it into con- 

 sent with the first, although there exist between them no 

 immediate nervous connection. Such is the sympathy 

 of the iris, when the retina is stimulated by light ; and 

 of the diaphragm during sneezing, when the Schnei- 

 derian membrane is irritated. 



There are other examples of sympathy, in which the 

 nerves, if they have any, have a more remote and ac- 

 cessory, share : J among these must be placed the sym- 

 pathy along the blood vessels, strikingly instanced 

 between the internal mammary and epigastric arteries, 

 especially in advanced pregnancy ; that along the lym- 

 phatic vessels, also most remarkable during pregnancy 

 and suckling ; and again, that dependent on analogy of 

 structure and function, v. c. the sympathy of the lungs 

 with the surface and intestines. (A) 



* G. Egger (the author Lawr. Gasser), De consensu nervorum. Vintlob. 

 176(J. 8vo. 



f J. G. Zinn's Observations, on the different Structure of the Human Eye 

 and that of Brutes. Diss. ii. 17,">7. Comment. Soc. Heir. Scitnt. dotting. 

 (tHtiq/iiftres. T. i. 



I Consider the constant sympathy of heat between certain parts of some 

 animals, v. c. of the hairs with the fauces, in variegated rabbits, sheep, dogs, &c.; 

 of the feathers with the covering of the bill and feet in varieties of the domestic 

 duck. That many such instances are not referrible to the influence of nerves, 

 1 contended in my Comm. de tnotu iriilia. p. 12 sq. and also in my work dc 

 generis humani varietate nntiva. p. 3(i4 sq. 



Innumerable pathological phenomena will be found explained by this sym- 

 pathy in S. Th. Soemmerring's De Morbis Vasorum Abwrb^ntium Diss 

 premium red/lit. Francof. 1795. 8vo. 



