CHANGES IN THE BLOOD. 95 



an extent that tlieir walls give way, and the blood is extra vasated 

 into the surrounding tissue. In this manner apoplexy of the 

 lungs is brought about, and so great is the extravasation in some 

 rare instances, that the blood has found its way into the bronclii 

 and trachea, and has been finally expelled through the nostrils. 

 The local constringing effect of cold is best witnessed upon the 

 human body, more especially in persons of weak circulation, in 

 whom, very often after washing or bathing in cold water, the 

 fingers are quite bloodless, pale, and numb. If we reason upon 

 this circumstance, and bring such reasoning to bear upon our 

 own subject, can we wonder that exposure to external cold is 

 followed by internal congestions. 



In many cases, however, nature provides a guard to the influ- 

 ence of cold uj^on the skin, by furnisliing animals with coats of 

 hair or wool suitable for their several necessities, and it is only 

 in animals wdiich are casually exposed to such cold that we 

 witness its effect in causing internal congestions. 



Congestion from diminished resistance arises from atony of the 

 wall of the vessels. This atony, loss of power, or relaxation of 

 the vessels, is generally due to paralysis of their muscular walls, 

 and most commonly occurs in vessels least provided with mus- 

 cular fibres, that is, in the capillaries and veins of organs easily 

 distended, and which are composed of much areolar tissue. This 

 paralysis of the muscular walls may be due to an influence opera- 

 ting upon the vaso-motor nerves, or to irritation of a sensory nerve. 

 Pressure upon the great sympathetic nerve in the neck causes 

 active congestion of the head and neck, and most probably the 

 congestion of the brain, redness of the conjunctivte, sufiusion of 

 tears, and other signs of fulness of the vessels of the facio-cranial 

 region, with the coma and delirium which are sometimes asso- 

 ciated with gastric or intestinal disease, are due to pressure upon 

 the cardiac branches of the gxeat sympathetic or ganglionic nerve. 

 It is very true that some emotions are attended with hypercTmia ; 

 and it may be said that the meningeal or cerebral congestion 

 of parturient apoplexy is due to some sympathetic influence 

 which the stomach has upon the brain. The question need 

 not be discussed here, as it will again come under considera- 

 tion; and let it suffice us for the present to know that dis- 

 order of the stomach is capable of producing congestion of the 

 brain. 



