CAUSES OF DISEASE. j 



outside world is maintained. Should, however, a 

 harmful influence be unusually strong, then the reac- 

 tions of re-adjustment to which it gives rise are corre- 

 spondingly vigorous and wide-spread, so that conscious- 

 ness is disturbed, functions are corrupted, and most 

 astonishing changes in the external appearance are 

 observed. These phenomena of reaction are evidence 

 of the battle that is being waged by the body against a 

 harmful force, and collectively they constitute the 

 symptoms oj disease. All harmful influences are pro- 

 vocative of disease ; yet disease does not exist unless the 

 reactions or symptoms are sufficiently pronounced as to 

 upset the orderly unconscious functioning of the body. 



Diseased states are also called morbid or pathological; 

 wherefore morbific or pathological causes are those 

 that bring about disease. The causes of disease are 

 often spoken of as agents. We divide the agents of 

 disease into four classes, mechanical, physical, chemical, 

 and animate. 



A blow which breaks a bone, an obstruction 

 Mechanical, to respiration due to a foreign body lodging 



in the larynx, a rupture of the abdominal 

 wall that permits a loop of the intestines to protrude, 

 are all instances of diseases due to mechanical agents. 



Similarly, alterations in the surrounding 

 Physical. medium, as for example, ascending to 



great heights, or working at great depths 

 under pressure, produce respectively mountain-climbers' 



