ETIOLOGY : CAUvSEvS OF DISEASE. 



Causes— simple — complicated : Proximate ; Remote : Predisposing — race, 

 genus, family, heredity, individual, environment, food, age, sex, tempera- 

 ment, idiosyncrasy, debility, plethora, interdependence of organs, embolism, 

 mechanical influence. Exciting causes, intrinsic, extrinsic, inherent, ac- 

 quired, heredity, dentition, heat, cold, atmospheric conditions, electricity, 

 moisture, dryness, dust, darkness, light, soil, food, water, inaction, over- 

 exertion, mechanical causes, poisons, — mineral — vegetable — animal, mi- 

 crobes, contagious, infectious, epizootic, enzootic, sporadic, panzootic, 

 zymotic, mediate contagion, bacterial poisons. 



The causes of disease are simple or complicated, and in the 

 latter case a single factor may be altogether harmless unless asso- 

 ciated with another which also may have been innocuous alone. 

 For example : the infecting germ of glanders (Bacillus Mallei) 

 is harmless to the ox which lacks the predisposition to the dis- 

 ease : — feeding buckwheat is harmless to the dark-skinned ani- 

 mal, but is injurious to the white-skinned, if exposed to sun- 

 shine :— the chicken can bear with impunity exposure to cold or 

 to the bacillus anthracis, but it cannot endure these two etiologi- 

 cal factors combined. It follows that one cannot predict the 

 same result from the same cause in every case. Yet with all con- 

 current conditions the same the result will follow with mathemati- 

 cal certainty. This will serve to illustrate the value of thorough- 

 ness in etiological knowledge, as the basis of a sound pathology. 



Etiology is primarily divided into proximate and remote. 

 Remote causes are again divided into predisposing and exciting. 



Predisposing Causes are such as induce a condition of the 

 system or of a particular organ or group of organs which renders 

 them specially susceptible to a disease. This may be a character- 

 istic of the race ox genus of animal, thus the genus bovis alone 

 suffers from lung plague, the genus equus from dourine, and 

 ruminants from Rinderpest. It may be a family trait, (^heredit- 

 ary) hence we .see certain families of both men and cattle cut off 

 by tuberculosis, while other adjacent ones largely escape. It may 

 be an individual peculiarity , thus some subjects have a congeni- 

 tal insusceptibility to a given disease, from which others of the 

 same family suffer, and one who has passed through a self-limit- 



