PREDISPOSITION TOWARD DISEASE 



Any living being becomes affected by disease when no longer 

 able to adapt itself to its environment and to the demands to 

 which the functional ability of its cells and organs is subjected. 

 As soon as such external influences exceed the limits of endur- 

 ance, as soon as they so affect the cells and organs as to induce 

 alteration of function, they become causes of disease. There is 

 really nothing upon which the animal body is dependent or with 

 which it is related, but may on occasion cause the onset of 

 disease — nutrimient, air, light, temperature, the various animal 

 and vegetable organisms about it. the varied accidents of nature, 

 its own active and passive relations, as well as every physiological 

 process going on in its economy ; and the very same factors, 

 which are generally essential for the maintenance of existence 

 and the well-being of the individual, may become agencies of 

 harm and noxious {nocere, to harm) influences productive of 

 disease. 



Whether the individual should experience the harmful possi- 

 bilities of such factors or not depends upon the inherited po- 

 tentiality of the organism, the functional capabilities of its cells 

 and tissues, and upon the efificiency of its protective and reg- 

 ulative mechanism. Sensitiveness to noxious influences, known 

 as Predisposition, and insensitiveness or insusceptibility, commonly 

 spoken of under the terms Resistance or Immunity, are by nature 

 widely different among different species and individuals and even 

 among the different tissues in the same animal ; and are subject to 

 considerable variations and abnormalities. The polar bear, the 

 Esquimau dog and the reindeer are accustomed to the cold of the 

 north, but sicken in the temperature of warmer climes ; many ani- 

 mals thoroughly adapted to the tropics, perish when transferred to 

 cooler regions even though furnished with their usual food. Indi- 

 vidual animals of the same species often manifest differences of 

 susceptibility, as where in herds of cattle or even, as is often ob- 

 served, in a number of cattle kept in the same stable, some path- 



