CHAPTER I. 



CHANGES IN THE CIRCULATION OF THE BLOOD. 

 Hypersexnia and Anaemia. 



THERE are several abnormal conditions of the circulation which at 

 death may either alter considerably or disappear altogether. Among 

 the more important of these conditions are hypercemia excess of blood 

 in a part ; and ancemia deficiency of blood in a part. These and the 

 conditions which lead to them will not be described in detail in this 

 book, which has chiefly to do with alterations of the tissue which persist 

 and may be studied after death. Tissues which have been the seat of 

 temporary, and sometimes of prolonged, hyperaemia, may not appear 

 abnormal after death, or they may look redder than normal ; they may 

 be redematous, and more blood than usual may flow from them when 

 incised. On microscopic examination the blood-vessels may be normal 

 in appearance, or more or less distended with blood. Long-continued 

 hyperaemia may lead to haemorrhage and trausudation, to pigmentation, 

 to hyperplasia of tissue, or to an atrophy of tissue through pressure, 

 or even to death of tissue. 



The paleness which is characteristic of anaemic tissues may not be evi- 

 dent after death. Anaemia may lead to no recognizable microscopic 

 changes. On the other hand, if long continued it may induce atrophy 

 and fatty degeneration, and, if excessive, may lead to death of tissue. 



Haemorrhage and Transudation. 



HEMORRHAGE. 



Haemorrhage is an escape of blood from the heart or vessels. It may 

 occur from a rupture of the walls of the vessels, and is then called haem- 

 orrhage by rhexis. The rupture may be occasioned by injury, by lesion 

 of the walls of the vessels which renders them too weak to resist the 

 blood pressure from within, or it may occur from the blood pressure in 

 the thin and incompletely developed walls of new-formed vessels as in 

 granulation tissue, tumors, etc. 



Under other conditions, without recognizable changes in the vessels, 

 all the elements of the blood may become extravasated by passing, 

 without rupture, through their walls. This is called haemorrhage by 

 (liapedesis. Such haemorrhages are usually small, but may be very ex- 

 tensive. They occur in the smaller veins and capillaries, the cells and 

 fluids of the blood passing out through the cement substance between the 



