128 DISEASES OF SWINE 



is forced out of the vessels by pressure and the redness disappears. 

 In those cases in which there is a genuine hemorrhage, with escape 

 of the blood from the vessels due to their rupture, pressure does 

 not remove the blood, and hence the redness does not disappear on 

 pressure. 



In these cases, if we were to examine the tissues from the skin 

 under the microscope we would find in the one class of cases — 

 those due to hyperemia — that there was simply a marked dilata- 

 tion and enlargement of the blood-vessels, which are filled with large 

 amounts of blood. There is in these cases, however, no escape of 

 blood from the blood-vessels into the surrounding tissues. 



On the other hand, in the hemorrhagic cases the microscope 

 shows us a different picture. The blood-vessels of the skin in these 

 cases are not only markedly dilated and engorged with blood, but 

 in many cases the pressure has become so great that the vessels 

 have given way under the strain, and there is a rupture of the ves- 

 sel wall, with the escape of the blood-cells into the tissues surround- 

 ing the blood-vessels. In this sort of change the redness produced 

 is permanent in character and cannot be removed by pressure. 



The location of these reddened areas on the skin is widely dif- 

 ferent in each individual case. In some cases it is practically im- 

 possible to find any reddened spots on the skin at all, especially 

 after death, as those spots which are due to simple congestion tend 

 to disappear after death. In other cases almost the entire skin is 

 reddened and spots of normal colored skin are difficult to find. 



However, there are certain locations of the skin where these 

 changes are most apt to be found, the following being the most 

 commonly involved: 



(1) The Ears. — The skin of the ears is one of the earliest spots 

 in which the red discoloration tends to appear. In addition to the 

 red coloring the ear also has a tendency to become markedly swol- 

 len and edematous or dropsical, due to the collection of a fluid in 

 the tissues under the skin. 



(2) The Eyelids. — The skin of the eyelids, and especially the 

 upper .lids, are also early involved in the changes produced, and 

 become reddened and swollen. 



(3) The Axilla. — This is the fold of skin extending from the 

 inner side of the foreleg to the wall of the chest. This skin is very 



