The _local effect of these specific irritants_, when they are not promptly attacked, devoured, and removed by phagocytes, is _pus_, which means cellular death, or gangrene, which is death of masses of cells which have not had time to separate from each other. Pus, then, is the ordinary consequence of the contest above alluded to, and _each pus cell represents the dead body of a phagocyte_ which has perished in the attempt to protect the parent organism from harm. That it has died valiantly can almost invariably be determined, because within its dead body may be seen one or more of the minute invaders which it has attacked. This, then, is the light in which inflammation and infection should be viewed. In other words, we may have escape of fluid portions of the blood, which may or may not coagulate; we may even have some escape of corpuscular elements with some activity in the extravascular cells, which shall lead to temporary or even permanent enlargement of a part; all of which may be provoked by injury or by the presence of certain chemical irritants within the blood or tissues; for example, alcohol, uric acid, etc. But the factors which provoke the greatest activity on the part of intravascular and extravascular cells, and which determine the richness in albumin of fluid exudates, or their prompt coagulation as soon as blood serum has escaped from the vessels, and which particularly determine the furious rush of phagocytes and that kind of intercellular conflict which leads many of the contestants on both sides to death, are living organisms which are introduced from without, whose presence at the point of inflammation is abnormal and injurious, which are offending substances in every respect, while the whole phenomenon of inflammation is an expression of an effort to rid the system thereof. Taking this view of the subject, there is an important distinction between hyperemia and its consequences, which is absolutely a non-infectious condition, and inflammation with its consequences, which is always an infection and is always followed by more or less death of cells, the same being often extruded in a semifluid mass known as _pus_. CIRCUMSTANCES WHICH FAVOR INFECTION. 1. =The Virulence of the Infecting Organisms and the Amount Introduced.=--There is the widest difference between various forms of microörganisms in the matter of virulence; and it is true that there are very great differences between the same species under different circumstances, these differences depending on conditions as yet absolutely unknown. With certain organisms it is enough to infect an animal with one alone in order to bring about a fatal result, this meaning that the organism itself is extremely virulent and the animal extremely susceptible.