DISEASE IN GENEHAL 191 



genetics. It should be understood that predisposition to is 

 vastly different from inheritance of disease . The latter condition 

 is seen in certain human families which for generations have 

 been susceptible to such diseases as insanity, goiter, asthma, and 

 deafness. Commonly a whole generation is skipped and the 

 disease does not appear for years. In other cases, the tendency 

 to disease is transmitted through the female side of the family 

 to the male as in color bhndness. While heredity does not 

 appear to play so important a part in the development of diseases 

 of domestic animals as of man, it is a factor in diseases of the 

 bones and joints of horses. 



Specific diseases, external mutilations, and all other acquired 

 characteristics cannot be transmitted to the offspring, as they are 

 not present in the germ cells. For example, it is common to crop 

 the ears of dogs, yet a breed of short-eared dogs is unknown. 

 Occasionally the newly born animal is found to be infected with 

 a specific disease, but in this case the disease was transmitted to 

 the fetus in utero and is not heredity in the biological meaning 

 of the term. Under such circumstances the newly born 

 animal acquires the same disease that the maternal parent is 

 affected with, e.g., tuberculosis of calf when cow has uterine 

 tuberculosis. 



(12) Autointoxication is a self-poisoning due to an accumula- 

 tion of poisonous substances in the body as a result of defective 

 elimination or faulty cell metabolism, such as irregularities in 

 digestion. When the digestive system fails to dispose of the by- 

 products promptly, they are absorbed and act as poisons to other 

 organs. The liver and kidneys, which normally throw off certain 

 waste products, are placed under too great strain. This results 

 in an inflammation of these organs and interference with their 

 functions. In the horse, azoturia is a notable example of auto- 

 intoxication due to an excess of nutrients in the blood. Fecal 

 toxemia due to constipation is a form of auto-intoxication, com- 

 mon in man, that is first noticed by headache and dullness. 

 Later all the excretory channels are overtaxed and the entire 

 body becomes poisoned and deadened. 



II. Determining Causes. — These causes operate directly to 

 produce disease and are accordingly known as direct, immediate, 

 physical, or exciting causes. They act more effectively if some 

 predisposing cause has first been operative. Sooner or later all 



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