DISEASE IN GENERAL 143 



produce disease. It is not uncommon to find certain animals in a 

 herd highly susceptible or predisposed to a specific disease while the 

 rest of the herd shows great resistance. Experience goes to show 

 that individual susceptibility is often due to "poor condition," 

 temporary physical depression, fatigue, exposure to cold, poor 

 hygiene, poisonous gases, etc. 



Constitution is an important factor in determining the resistive 

 influences possessed by the body against disease. A horse is 

 said to have a "strong constitution" when his resistive powers are 

 highly developed, and a "weak constitution" when he is susceptible 

 to the influence of his surroundings. An individual may have 

 much resistance against many types of disease influences and yet 

 be weakly constituted in some way. The strength of general con- 

 stitution is measured by the strength of the least resistive ability, 

 like the strength of a chain is that of its weakest link. 



Condition is that ideal state of the body which renders it fit 

 for work. It is recognized principally by the rotundity and ful- 

 ness of development. The term is frequently used by horsemen, 

 and has come to signify the perfection of bodily health and vigor. 

 An animal is said to be in the "pink of condition" when all the 

 organs are working in harmony. The expression probably origi- 

 nated from the fact that the visible mucous membranes of healthy 

 animals are always a delicate pink color. It is impossible to over- 

 emphasize the importance of condition in warding off disease. 

 The common causes of putting an animal "out of condition" are 

 similar to those mentioned as the causes of disease, only in a lesser 

 degree. They include overfeeding, insufficient work, too much 

 work, or too much work combined with insufficient food, and the 

 result of lameness or sickness. 



The facts detailed above explain why a given micro-organism 

 may cause a fatal infectious disease in one animal but may pro- 

 duce only a moderate sickness, or cause no damage whatsoever, in 

 another. 



THE SYMPTOMS OF DISEASE 



We have seen how disease modifies the body. It should not 

 be supposed, however, that it is possible to distinguish closely 

 between disease and health, or that one is just the opposite of the 

 other. As a matter of fact, the two conditions blend almost in- 

 sensibly. Only when an organ or group of organs is affected to 



