CAUSES OF INFLAMMATION. 15 



and exciting causes : — 1st. Predisposing causes are influences 

 not of themselves essentially irritant, yet often co-operate with 

 others in inducing the inflammatoiy process. They may be 

 summarised as follows — debility either of an organ or of the 

 whole body arising from old age ; previous disease or a natural 

 weakness ; hereditary taint or predisposition ; obstruction of 

 the blood-vessels ; plethora ; climatic influences ; dietetic errors ; 

 insufficient ventilation, and ill-treatment of all kinds. 



2d. Exciting or determining Causes. — These are agents which, 

 if powerful, will of themselves be sufficient to determine 

 the inflammatory process even in healthy tissues, but which 

 will do so with more certainty in parts predisposed. They 

 may be arranged as follows : — Direct violence ; the appli- 

 cation of irritants ; exposure to heat and cold ; the presence of 

 foreign bodies, or of parts deprived of life ; retained concretions 

 or excretions; abnormal conditions of the blood, as in rheumatism 

 and anaemia, or when containing some irritating ingredient, mor- 

 bid or specific virus, or poisonous drug. I think Dr. Burdon 

 Sanderson simplifies the causes and origin of inflammation very 

 much. He says — " With reference to their origin, all inflam- 

 mations may be comprised in two classes — extrinsic and in- 

 trinsic. Of these two terms, the former is applicable to all those 

 cases in which an injury, either sustained by the affected part 

 or inflicted elsewhere, is the obvious cause of the morbid process ; 

 the latter to those inflammations which, from the concealment 

 of their cause, are commonly called idiopathic. If, however, we 

 desire to speak accurately, we must discard this word altogether ; 

 for there is no case in which it can be reasonably doubted that 

 an injury must have preceded the earliest sign of local disorder, 

 however little we may know either of the nature of the agent 

 or of the mode of its action. We might advantageously sub- 

 stitute for idiopathic either of the words intrinsic or secondary ; 

 but inasmuch as there is no channel by which an agent from 

 within, i.e., from some other part of the body, could penetrate 

 into a tissue, excepting by the blood-vessels or lymphatics, we 

 are entitled to use the only word which fully expresses this 

 view of the mode of introduction of the material cause, and to 

 designate all so-called idiopathic inflammations infective. 



" From what has been said it may be readily understood that 

 the primary inflammations naturally affect those parts princi- 



