70 CHANGES IN THE BLOOD CIRCULATION. 
What is hemorrhage and how does it take place ? 
It is an escape of blood from the heart or bloodvessels and may take 
place by rupture (or rhexis) or by diapedesis. 
How is hemorrhage by rupture produced ? 
Hither by external injury, or the walls of a bloodvessel become so 
weakened by disease that the pressure of blood within is enough to 
rupture them. 
Describe rupture by diapedesis. 
There is no appreciable change in the vessel-wall, but it is supposed 
that through some change in nutrition the vessel-walls are weakened, 
and that the white-blood cells, partly by virtue of their amceboid 
motion, pass between the cells lining the vessel. The red-blood cells 
have no power of motion and are thought to be carried passively 
through the endothelial cement substance by minute currents of fluid 
which follow the white-blood cells. 
What are the terms applied to the different forms of hemorrhage ? 
Petechiz—very small hemorrhages. 
Ecchymoses or Suggillations—larger, diffuse hemorrhages in the 
interstices of a tissue. 
Hemorrhagic Infarction—a complete infiltration of a circumscribed 
_ portion of tissue with blood. 
Hematoma—a circumscribed collection of blood in a tumor-like mass. 
What are thrombi ? 
They are masses made up of different elements of the blood mixed 
in varying proportions. They are produced in the heart or vessels by 
the coagulation of blood incited by injury or disease. When lying 
against the wall of a vessel they are called parietal thrombi, and when 
entirely filling a vessel are called obliterating thrombi. 
What changes occur in thrombi ? 
They may soften,-break up and be carried into the circulation. 
They may degenerate, become infiltrated with lime salts, and are then 
called phlebolites or vein stones ; or, they may organize and form new 
connective tissue. 
What is an embolism ? 
It is a stoppage of a bloodvessel by some mass of material (larger 
than the lumen of the vessel) which has been carried along in larger 
bier irs in the circulating blood. The obstructing mass is called an 
embolus, 
