ETIOLOGY— CAUSES OF DISEASE 215 



PREDISPOSING CAUSES OF DISEASE 



The predisposing causes of disease are generally subdivided under 

 several headings, which may begin with the hereditary constitution, which 

 is the most prominent and important, then temperament, age, sex, &c. — 

 these are all intrinsic, existing within the body independently of any 

 influence from without; then follow a number of extrinsic predisposing 

 causes, such as excitement, occupation, and conditions which induce debility. 



Excitement may be looked upon as a predisposing cause of disease 

 when it leads to excessive development of activity in the circulatory and 

 nervous systems associated with general or systemic excitement — a con- 

 dition which may stop short of actual disease, but is especially favourable 

 to the action of any exciting causes which tend to set up inflammation. In 

 a state of general excitement the system is liable to suffer from any febrile 

 disease which may be at the time prevalent, or from sudden exposure to 

 violent changes of temperature, which may lead to an inflammatory attack. 

 Certain forms of local excitement lead to the determination of blood to 

 a particular part, which may end in the rupture of vessels, or may increase 

 the functional activity of a part and thus render it liable to any influence 

 from without or within which may induce congestion or inflammation. 



Excitement may in itself result in the development of active inflam- 

 matory disorders without the intervention of any extrinsic cause, in which 

 case it would be classed among the exciting causes of disease. For the 

 present purpose it is only to be looked upon as acting to a sufficient degree 

 to render the system susceptible to disease without actually inducing it. 

 It is in the nature of things, in fact, that predisposing and exciting causes 

 very frequently approach each other so closely that it is impossible at all 

 times to distinguish the one from the other. 



Debilitating influences, whether arising out of insufficiency of food 

 or feeding to excess, will both have the effect of reducing the vital energy, 

 and in this way diminishing the power to resist disease. Insufficient food 

 is the most common cause of debility acting in a perfectly intelligible way, 

 not only by a failure to supply a sufficient amount of nutriment to com- 

 pensate for the waste of the tissues, but further by inducing a feeble 

 condition of the digestive powers as a mere consequence of inactivity. 

 Excess of food induces a similar result through the medium of the opposite 

 conditions, the nutritive functions become impaired as the result of con- 

 gestion of the vessels which supply the digestive organs with blood, and 

 consequent overwork and derangement of the secretive and excretive 

 processes. Further, mischief is done by an excess of nutritive material 

 beyond the amount which the system is capable of appropriating, the excess 



