232 PRINCIPLES OF VETERINARY SCIENCE 



It is the reaction which living tissues show almost immediately 

 to an injury or an irritant. 



The term irritant may be best understood by first learning 

 what is meant by a stimulant. A stimulant is anything that 

 produces action in a living tissue, like the application of a mild 

 liniment to the skin. When excessive stimulation is applied, 

 like a very strong liniment or blister, irritation or injury results. 

 Irritants and stimulants, therefore, differ only in the degree of 

 action which they produce in the tissues. 



The changes in inflamed tissues consist of a series of processes 

 entirely similar to those taking place under normal conditions, 

 only in more marked degree. Much blood is brought to the 

 part. Besides nutritive substances, the blood brings a whole 

 army of leukocytes to attack the irritant, neutralize its poisons, 

 and prevent further injury. 



The causes of inflammation include a great variety of mechan- 

 ical, thermic, chemical, electric, and infectious agents. When 

 these agents produce injuries they always destroy some cells. 

 The dead cells act as irritants, consequently they set up an inflam- 

 mation. The first four of these causes may be classed as non- 

 bacterial in character, and produce an aseptic or non-infectious 

 inflammation. The infectious agents consist of microorganisms 

 which set up a septic or infectious inflammation. When the 

 virulence of the invading bacteria is great, there results a rapid 

 general infectious process with fatal termination; on the other 

 hand, when the microorganisms are of low virulence, there 

 occurs a slowly developing inflammation, which may be overcome 

 by the bactericidal substances of the body before much damage is 

 done. 



The kinds of inflammation depend upon the character of the 

 exudate produced. The simplest kind is a serous inflammation, 

 in which a watery exudate like the contents of a water-blister is 

 formed. A suppurative inflammation is accompanied by the for- 

 mation of pus; a good example is an abscess. A productive or 

 proliferative inflammation is the kind most common in bone tissue, 

 like ringbone and spavin growths. Croupous and diphtheric in- 

 flammations occur on mucous membranes. 



The course of inflammation is determined by the rapidity and 

 intensity of the process in the inflamed tissue, and may be either 

 acute, subacute, or chronic. 



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