CHAPTER X 

 INFLAMMATION 



ALTHOUGH morphological alterations are prominent features 

 of the reaction of the tissues to local injury and infection, yet 

 at the bottom the processes of inflammation are brought about 

 by and result in chemical alterations. The causes of inflamma- 

 tion are in nearly all cases chemically active substances, but for 

 the most part their nature is too little known to permit of 

 speculation as to what chemical characteristic or characteristics 

 a substance must possess to exhibit the power of causing an 

 inflammatory reaction. Even in the case of inflammation due 

 to mechanical, thermal, and electrical injuries, it seems probable 

 that most of the features of the inflammatory reaction are 

 brought about by the action of chemical substances produced 

 by alterations in the tissue constituents at the point of injury. 



The essential features of inflammation, namely, local hyper- 

 emia and related vascular disturbances, exudation of plasma, 

 migration of leucocytes and their phagocytic action, all may be 

 caused by the action of chemical substances upon the vessels and 

 leucocytes. Active hyperemia in the case of inflammation is due 

 to stimulation of the vasodilator nerves or paralysis of the vaso- 

 constrictors, or direct paralysis of the muscular fibers of the 

 arterioles ; these may result from mechanical, thermal, or 

 electrical stimuli, but in local infection the cause is usually 

 chemical products of bacterial growth or of tissue disintegra- 

 tion. The escape of blood plasma (inflammatory edema) appears 

 to depend upon a number of factors (discussed more fully under 

 "Edema/ 7 Chap, xii) of which the most important seem to 

 be : (1) injury to the capillary walls, produced largely by the 

 chemical causes or products of the inflammation ; (2) increased 

 osmotic pressure in the tissues, due to increased or abnormal 

 formation of crystalloidal substances with high osmotic pressure 

 from large molecular compounds, many of which are colloids 

 (proteids) without appreciable osmotic pressure. By far the 

 most characteristic feature of inflammation, however, is the 

 behavior of the leucocytes their increase in number in the blood, 

 their migration from the vessels and accumulation about the 

 point of injury, and their engulfing and destroying various 



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