CAUSES OF DISEASE 



The influences Avhich lead to bodily injury, to pathological 

 lesions, and which are spoken of collectively as disease causes 

 (causer uwrhi) may be arranged in a number of classes. 



There are influences dgainst which the strongest and most 

 resistive constitution is powerless and which inevitably induce 

 disease in the animal coming under their action ; such absolute 

 pathogenic influences include mechanical forces, intense thermic 

 and electric agencies, mineral and vegetable poisons in their 

 higher dosage and concentration, and, provided they can gain 

 entrance to the intracorporeal structures, various animal para- 

 sites, bacteria and [animal] microorganisms. Other harmful 

 agencies are pathogenic only under special circumstances and 

 are therefore only relative, depending, for example, on the 

 quantity of the exciting agent, or upon special predisposi- 

 tion of the subject or upon the concurrence of several harmful 

 influences {relative causes of disease). The occasion which brings 

 a harmful influence in relation with the body or subjects the 

 latter to such influence, is spoken of as the predisposing cause 

 (causa proximo). The principal factor in producing a lesion is 

 known as the special, immediate or essential cause of disease 

 (causa essentialis) ; among these it should be understood that 

 either external harmful agencies which have gained entrance into 

 the body or which operate upon it from without, or some already 

 existing tendency toward disease may be included. For example, 

 pasturing upon some upland infested with anthrax affords the 

 opportunity by which the anthrax bacillus as the essential cause 

 of anthrax gains entrance to the body ; an injury, the favoring 

 condition for wound infection by the essential cause of tetanus. 

 Anything which promotes the action of an injurious agent may 

 be regarded as a contributary cause (causa auxilians). 



Pathological influences may be divided into the following 

 groups : 



