26 OF THE VITAL. POWERS. 



The primary and most extensive cause of sympathy 

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

 the semorial reaction ;f 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. Vindob. 

 17C6. 8vo. 



t J- G. Zinn's Observations on the different Structure of the Human Eye 

 and that of Brutes. Diss. ii. 1757. Comment. Soc. Reg. Sctent. GottHtg. 

 antiquiores. T. i. 



X 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 rcferriblc to the influence of nerves. 

 1 contended in my Cotnm. de motu iridis. p. 1*2 sq. and also in my work de 

 generis hutnani varietate nativa. p. 364 sq. 



§ Innumerable pathological phenomena will be found explained by this sym- 

 pathy in S. Th. Soemmerring's De Aforbis Vasorum Absorbentiuin Diss, jimp 

 jiramium retultt. Francof. 1 796. 8vo. 



