Active Hypcrmnia. 113 



nervous apparatus comprises two types of nerve fibres, vasodilator 

 and vasoconstrictor ; theoretically, therefore, stimulation of the 

 vasodilator nerves should occasion a widening of the blood chan- 

 nels (neurotonic congestion), and the same result should follow 

 paralysis of the vasoconstrictors (neuroparalytic congestion) , both 

 of these influences similarly reducing the tension of the muscular 

 elements of the arterial wall. This relation with nervous influ- 

 ences is well seen in the fact that after section of the cervical 

 sympathetic in rabbits the ear on the corresponding side becomes 

 hypergemic (CI. Bernard), and after section of the splanchnics the 

 vessels of all the abdominal viscera become distended and engorged 

 with blood (paralysis of the vasoconstrictors). Stimulation of the 

 nervi erigentes of the human penis causes a dilatation of the 

 arteries of the organ ; blushing in man is brought about by psychic 

 influences upon the dilator centre through reflex action ; certain 

 poisons, as nicotine and alcohol, are apparently stimulating to 

 the dilator centre. Generally the stinmlation or paralysis of the 

 vascular nervous apparatus indicated is the direct result of local 

 influence by physical or chemical agents. Thus hypergemia may be 

 induced mechanically by the removal of pressure acting upon the 

 vessels ; just as a sponge which has been squeezed and is then 

 released takes up water, so the blood flows in large amount, imme- 

 diatelv after removal of the pressure, into a tissue which has been 

 deprived of its blood for a long time because of compression. The 

 vessels here do not at once regain their contractility, but are 

 relaxed. 



Similarly friction and scratching can induce hyperemia 

 mechanically, from the nervous stimulation thus originated. 

 Thermic influences of both types give rise to hypcnemia ; heat by 

 its direct relaxing influence upon the vessel walls, cold first 

 causing a vasoconstriction which later gives place to a paralyysis 

 of the vascular musculature. There is a special group of chemical 

 irritants as oil of mustard, cantharides, ammonia, alcohol, chloro- 

 form, ether, saline solutions, which, either by stimulating or 

 paralyzing the nerves of the vessel walls, cause a more or less 

 intense arterial hyperaemia ; these, because of the value of the 

 hyper?emia in the treatment of various affections, are of therapeutic 

 importance (rubefacients, drugs which cause reddening of the 

 skin). Probably in the erythemata which occur in various infec- 

 tious diseases there also exists a similar toxic stimulation or 

 paralysis of the vessel walls either from the bacteria or the 

 microbic products. 



