Hyperemia. Congestion. 37 



■ Symptoms and results. If on a mucous membrane or white 

 skin the color becomes dark red, or violet (cyanotic) with evident 

 distension of the capillaries and veins, the latter of which may 

 stand out as knots or cords, there is an appearance of swelling or 

 enlargement and sometimes coldness of the part. Soon the wa- 

 tery part of the blood transudes in excess, constituting dropsy, 

 with increased swelling and pitting on pressure. On the mucous 

 surfaces it determines an abundant serous secretion. The color 

 is deepened by the escape from the vessels of red globules as well 

 as white.. The transudation contains little albumen and only 

 exi;eptionally fibrine. In connection with the marked deoxidation 

 and high carbonisation of the blood, the nutrition of the part is 

 largely arrested together with the functions, secretory, motor or 

 otherwise. The imperfectly nourished vessels may give way, 

 leading to haemorrhage, or nutrition may be definitely arrested 

 producing moist grangrene or ulceration. Sometimes a thrombus 

 is formed in a congested vein. The changes in the affected 

 organs depend much on the degree and duration of the hyperse- 

 mia: If slight and lasting it causes permanent induration and 

 thickening, from connective tissue hyperplasia as frequently seen 

 in the hind limbs of the horse. In case of blood transudations 

 the altered coloring matter gives the various shades of gray, 

 brown or black. If long continued the organ may shrink and 

 atrophy occur from defective nutrition and contraction of the 

 fibrous hyperplasia. 



In making post mortem examinations mistakes may be made 

 through the occurrence of changes after death. Thus a hyperse- 

 mia which was quite considerable during life may virtually disap- 

 pear through the contraction of the arterial and capillary coats, 

 forcing the blood on into the veins. A minute point of extrava- 

 sation here and there may be the only macroscopic lesion left. 

 Again a marked venous and capillary hyperaemia in a dependent 

 part of the body or of an organ may be entirely due to hypostatic- 

 conditions, the blood having settled into the lowest part of the 

 vessels since the death of the animal. To avoid this source of 

 error one must always carefully note the position of the carcass 

 after death. Under other circumstances the superficial veins and 

 capillaries may fill up with blood through the occurrence of de- 

 composition and the evolution of gases in the internal cavities^ 

 which empty the splanchnic and parietal vessels by compression. 



