114 Disturbances of Circulation. 



Active hypersemia is essentially an arterial and capillary dilata- 

 tion. The hyperaemic organ or tissue therefore manifests as one 

 of its features a red color, which is the more striking the paler the 

 tissue normally is, as in mucous and serous membranes, and may 

 be so pronounced that the distended arteries appear as fine deep- 

 red lines (branched or injection erythema). The rapidity of the 

 flow of the blood into and through the involved area, with but 

 little output of its oxygen, causes it to remain bright red and 

 pass thus into the veins. In peripheral parts of relatively lower 

 temperature previous to the increased blood supply, there is a rise 

 of temperature up to that of the blood. These peripheral parts, 

 particularly the skin, because of their greater heat loss and their 

 comparatively poor blood supply are lower in temperature than the 

 internal organs ; but with the access of more blood of the body 

 temperature the skin with its rate of heat dissipation unchanged 

 necessarily becomes warmer. The temperature attained does not, 

 however, exceed that of the internal organs ; and these, should they 

 become hyperaemic, do not suffer any increase of temperature. 

 \\'here there is marked capillary distension, provided the tissues 

 are not rigid, there ma}- also be induced some swelling. 



The results of arterial hyperemia vary with its duration and 

 location. Hyperaemia of the brain is followed by unimportant or 

 marked disturbances of consciousness, dizziness and general excita- 

 tion (pressure of the engorged vessels on the nervous elements). 

 Hyperaemia of the sympathetic nerve does not cause either lachry- 

 mation or salivation, and it is doubtful whether an uncomplicated 

 hyperaemia causes any special lymph formation. In case of long 

 continuance of the hyperaemia there becomes apparent an increased 

 tissue proliferation ; this is probably not due to the increased blood 

 supply alone, the irritant which underlies the condition having also 

 in all likelihood some stimulative influence in its causation. 



As a rule uncomplicated hyperaemia is a transitory condition ; 

 with the disappearance of the cause for the vascular relaxation the 

 contractility of the arteries returns. Otherwise the hyperaemia 

 may be regarded as the precursor and concomitant of inflammation. 

 Where large amounts of blood are drawn into extensive areas of 

 hyperaemia, a deficiency of blood (collateral anaemia) may be occa- 

 sioned in other regions. 



Where the excess of blood exists in a part because of difficulty 

 in its exit from the part it is known as passive hyperaemia or 

 venous engorgement. This condition is encountered in connection 



