28 JOURNAL OF THE [January, 



producing a congestion of the parts, from which the impulse 

 originates. This abnormal blood supply increases the nutrition 

 of the mucous membrane, giving rise to a hypersecretion of the 

 mucous glands. 



The blood-supply of the body is regulated by the great sym- 

 pathetic nervous system, which surrounds the arteries, and the 

 sympathetic nerve-endings are supposed to terminate in the 

 muscular coats of the arteries. Any thing, which affects this 

 system of nerves, will cause either contraction or dilatation of 

 the vessels, thus diminishing or increasing the blood-supply of 

 the part. A common illustration of this fact is shown when, on 

 approaching a hot fire, the skin becomes red, and the action of 

 the heat on the nerves of the skin causes the capillary blood- 

 vessels to dilate, and thus increasing the action of the sweat 

 glands, the surface becomes moist. In the same manner the 

 application of cold to the surface causes contraction of the 

 capillaries. Stimulation of certain nerves, connected with any 

 organ or tissue of the body, will cause a determination of blood 

 to those parts, and a hyperactivity. 



The amount and continuance of a congestion, or hypersemia, 

 depends on the duration, rather than on the amount of irritation 

 present. A severe cut on the surface of the body, with some 

 sharp instrument, causes local hyperaemia of the surface incised, 

 while it is comparatively of short duration ; while the prolonged 

 presence of a splinter, or other foreign body, will cause severe 

 inflammation, which may ultimately end in gangrene. Such 

 illustrations show the influence of the nerves over the arterial 

 system, and demonstrate to us that the nerve-theory of Hay- 

 Fever is not altogether unfounded. 



It may easily be seen from the above facts, how certain sub- 

 stances, coming in contact with the mucous surfaces of the nose 

 and throat, will set up an irritation in the terminal nerve-fibres ; 

 and how this irritation, in the form of nerve-impulses, keeps 

 flashing along the sensory nerves to the switch-men in the 

 medulla, who, in the form of nerve-centres, having no action of 

 their own, irrespective of events taking place elsewhere in the 

 body, receive their elective despatches, and faithfully transmit 

 them down the cervical spine, and, by means of the cervical 

 sympathetic system, dilate the nasal and pharyngeal capillaries, 

 thus causing the familiar discharges from the nose and throat. 



