HYPEREMIA 313 



case of irritants, such as alcohol, ether, ammonia, mustard, etc., which 

 act neither by producing; a local vasodilator stimulus or Ijy paralyzing 

 the vasoconstrictors. Other substances may produce active hypere- 

 mia in special vascular areas, e. gr., cantharides causes active hyperemia 

 in the kidneys, probably because of its elimination through these 

 organs; pilocarpin causes active hyperemia in the salivary glands and 

 skin, which is associated with increased function. In general, func- 

 tional activity is associated with active hyperemia, and GaskelP^ has 

 suggested that this is due to atonicity of the vascular muscle, the result 

 of decreased alkalinity of the lymph flowing away from the active organ 

 along the vessel-walls, it having been found that alkalies cause a tonic 

 contraction and acids an atonic dilation of arterial muscle. '" 



Pathological active hyperemia is seldom of long enough duration 

 to lead to any alterations in the tissues in which it occurs. The blood 

 itself remains unchanged, except that the venous blood going from the 

 part contains much less CO2 and more oxygen than usual, because 

 more oxygen is brought to the tissues than can be used.'*^ 



Passive Hyperemia 



Passive hyperemia is almost equally unassociated with chemical 

 changes, especially in its etiology, as it depends solely upon mechan- 

 ical factors. Some chemical alterations result, however, from the 

 changes in the stagnating blood, wliich may, if the obstruction to out- 

 flow is severe, become of venous character in the capillaries of the con- 

 gested area. Oxidation in the tissues is, therefore, impaired, and some 

 fatty changes may result, e. g., in the center of congested liver lobules. 

 Waste products accumulate, and possibly noxious products of meta- 

 bolism are formed under lack of oxidation; either from these causes or 

 solely from pressure and lack of nutrition there is a tendency to atrophy 

 of the more specialized parenchymatous cells, and a proliferation of 

 connective tissues. The atrophy of parenchyma is seen particularly 

 in the liver, the increase of connective tissue in the spleen. ^^ In the 

 Ividney neither atrophy nor stroma proliferations are pronounced, but 

 the renal function is greatly impaired, since it depends upon the 

 amount and quality of the blood brought to the kidney.""^ Whether 

 connective-tissue proliferation in hyperemia depends upon overnutri- 

 tion or upon irritation by waste-products, or is compensatory to par- 

 enchymatous atrojihy, may be looked upon as still an open question. 



*^ Quoted by Lazarus-Barlow, "Manual of General Pathology," 1904, p. 126. 



"See discussion by WooUey, Jour. Amer. Med. Assoc, 1914 (63), 2279; and 

 by Adler, Jour. Pharm., 1916 (8), 297. 



" Polycythemia (Vaquez-Osler disease) is accompanied by an increase in the 

 total nitrogen of the blood, in proportion to the number of erythrocytes; but the 

 nitrogen content of the individual erythrocyte is decreased, (v. Jaksch. Zent. 

 inn. Med., 1912 (33), 397). 



*^ See Christian, Jour. Amer. Med. Assoc, 1905 (45), 1615. 



" See Rowntree and Geraghty, Arch. Int. Med., 1913 (11), 121; Nonnenbruch, 

 Deut. Arch. klin. Med., 1913 (110), 162. 



