GENERAL PATHOLOGIC CHANGES 159 



acter of blood or destroy the corpuscles, may be responsible for 

 ascites. The chief symptoms are distention of the belly and 

 marked swelhng of the hmbs. Treatment consists in abundant 

 nutritious food, iron tonics, and drugs to act on the kidneys to 

 induce the urine to flow more freely. Tapping the animal to 

 permit the fluid to escape is often necessary, but affords only tempo- 

 rary relief. 



Hydro thorax is a complication of certain forms of pleurisy. It 

 is characterized by an accumulation of fluid in the thoracic cavity. 

 When present this form of dropsy may be diagnosed by tapping 

 the lower part of the chest wall. If the ear is placed over the 

 chest a sound resembling that of drops of water falling into a well 

 may be heard. 



INFLAMMATION 



Inflammation is the one constant factor in all pathologic changes. 

 By its aid the body overcomes disease, heals wounds, and unites 

 fractured bones. It has been defined as the highly complex react- 

 ive process which living tissues show to an irritant. 



The term "irritant" may be best understood by first learning 

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

 duces action in a living tissue, like the application of a mild lini- 

 ment to the skin. When excessive stimulation is applied, Hke a 

 very strong liniment or blister, irritation 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 physiologic procedures, only in more marked 

 manifestation. Besides an increase in the nutritive substances 

 brought to the part, there is mobilized a whole army of leukocytes 

 to attack the irritant agent and neutralize its poisons. 



The causes of infianunation include a great variety of mechan- 

 ical, thermic, chemical, electric, and infectious agents. Examples of 

 each are seen on all sides. The first four of these causes may be 

 classed as non-bacterical in character, and produce an aseptic 

 or non-infectious inflammation. The infectious agents consist of 

 micro-organisms which set up a septic or infectious inflammation. 

 Depending upon the virulence of the invading bacteria, there re- 

 sults either a rapid general infectious process with fatal termina- 

 tion or, where the micro-organism is of lower virulence, a slowly 



