■2U HEALTH AND DISEASE 



a departure from the ordinary normal or healthy condition of the structures 

 or functions. Certain forms of bony tumours which occur in situations 

 where they do not interfere with the mechanism of the skeleton, and are 

 unattended with pain or inconvenience, may be referred to in illustration 

 of this proposition. 



Pathology includes everything connected with a departure from 

 health, and implies, therefore, a wide range of knowledge in regard to all 

 the circumstances under which structural or functional changes are 

 developed. Etiology is a division of the science of pathology which relates 

 to the causes of disease. Semiology refers to symptoms or indications, or, 

 in other words, to the external expressions of a morbid condition. Predis- 

 posing causes are those which, as the term implies, act injuriously upon the 

 organism and render it liable to the influence of more energetic causes. 

 Various circumstances of an ordinary kind, such as changes of temperature, 

 exertion, quality and quantity of food, the impurities in the atmosphere, 

 age, sex, conformation, temperament, and hereditary disposition may all be 

 classed as predisposing causes of disease. Nosology is the classification of 

 disease. Diagnosis implies the accurate definition of a disease, its position, 

 nature, and localization. Prognosis relates to the probable termination of 

 disease, or the expression of the opinion of the observer based upon his 

 diagnosis; its value necessarily depends upon his experience of the course 

 which the disease has taken in similar cases, or upon the accuracy of his 

 judgment in regard to the actual morbid changes in the structures or func- 

 tions in the particular case under consideration. 



ETIOLOGY— CAUSES OF DISEASE 



The most obvious and at the same time the most simple and practical 

 classification of causes of disease is the division into Predisposing and 

 Exciting. This classification includes at. once nearly all that can be said 

 on the subject of causation. Various subdivisions are for convenience 

 employed, but they all relate as a matter of necessity to the two primary 

 divisions, for example, extrinsic and intrinsic causes, in other words, causes 

 acting from without and those which arise within the animal body and 

 which may cither increase the tendency to acquire the disease or may 

 actually cause its development. Specific causes occupy a position which 

 in some degree disconnects them from ordinary causes whether predisposing 

 or exciting. The term specific indicates that there is something peculiar 

 to be taken into account, and at the present day the term is limited to 

 those causes of disease which include some particular micro-organism 

 or some specific poison, which may be either extrinsic or intrinsic. 





