416 FUNCTIONS OF THE NERVES. [ch. hi. 



unknown, recurring periodically, and thus produce the derivation 

 of blood to the uterus. Probably it is some latent peculiarity 

 of the vis nervosa, which recurs periodically, and causes a deriva- 

 tion of blood to the uterus, just as we observe intermittent fevers 

 to return periodically. 



Not only is dilatation of the minute radiated vessels of the 

 iris produced by congestion, but also elongation and deflection 

 from a serpentine to a straight line, in consequence of which 

 the iris is dilated and the pupil contracted, when the retina is 

 irritated by a strong light, and this again acts on the ciliar,y 

 nerves by consentience.^ The cause ceasing, which through the 

 nerves induced congestion, the congested fluids appear to be 

 driven into the larger vessels by the elastic and tense capillaries, 

 and thus the minute radiated vessels of the iris are again short- 

 ened, and arranged in serpentine folds, and so the iris is con- 

 tracted and the pupil dilated. 



By a similar but greater accumulation of blood in the cor- 

 pora cavernosa of the penis and clitoris, excited by the nerves, 

 these parts become turgid, hard, and erect, when their nerves 

 are excited, either locally by a mechanical stimulus, or by 

 lascivious ideas.^ 



Thus also the papillae of the mammae swell, become hard, 

 and those which are retracted into their fossae protrude, when 

 rubbed with the tip of the finger, or taken within the lips of 

 the infant, because their nerves being vellicated, excite a greater 

 flow of fluids into the vessels (for a corpus cavernosum is not 

 found in them), and produce the whole phenomenon.^ 



That appearance of the human skin termed cutis anserinaj 

 arises also from a greater derivation of the fluids caused by the 

 cutaneous nerves, for the spongy bulbs of the hairs become 

 turgid by the blood attracted more copiously to them, and pro- 

 duce those small eminences on the skin, from which the term 

 cutis anserina is derived, and by which also the hairs proceeding 

 from them are rendered erect. When that greater derivation 



» Haller, *Elem, Phys.,' torn, v, lib. xvi, sect, ii, § xii; Caldani, 'Instit. Physiol.,' 

 Nro. 320 ; and my tract, • De Carne Muscular!,' may be consulted, p. 10. 



2 Caldani, loc. cit., Nro. 494 ; Winterl, ' Inflamm. Theor. Nov.,' p. 143. 



' Kolpin's Dissertation, * De Structura Mammarum,' may be consulted, translated 

 into German (Berlin, 1767), p. 16, where the translator in a note supposes a con- 

 gestion of humours into the irritated part, by oscillation of the vessels increased 

 through the nerves. 



