me "begin by defining our terms. Pathology (literally, a 

 discourse on pain) may be defined as the. science which treats 

 of the origin, nature, course, and causes of those changes in 

 the body which constitute disease, or as the physiology of 

 disease. What, then, is meant by the term disease ? " By 

 disease is understood some deviation from the state of health ; 

 a deviation consisting for the most part in an alteration in 

 the functions, properties, or structure of some tissue or organ, 

 owing to which its office in the economy is no longer per- 

 formed in accordance with the normal standard." 1 Diseases 

 .are generally regarded as consisting of two classes viz., 

 organic and functional The terms health and disease are 

 .alike relative and indefinite ; neither health nor disease being 

 separable from each other by any hard and fast line, and the 

 one passing into the other by insensible degrees, just as 

 physiology passes insensibly into psychology. Disease is 

 then, generally, an abnormal performance of the vital pro- 

 cesses nutrition and function^ the latter being especially 

 dependent upon the state of the former. When, therefore, 

 both of these processes are normal, the condition is one of 

 health ; when abnormal, one of disease. Diseases are, there- 

 fore, not entities, but mere groups of modifications of 

 structures already in existence, and of actions always pro- 

 gressing in a vital system. They are, in fact, particular 

 conditions of the living body new phases of its vital mani- 

 festations whether of the nature of functional derangements, 

 or of organic or textural degeneracy. Sir John Forbes says : 

 " All morbid action is but a modification or perversion of 

 .some natural or normal action or function; and all the 

 physical results constituting morbid structural alterations are 

 mere perversions or modifications of natural or normal 

 Green's "Pathology." 



