HEREDITY OF DISEASES. 25 



defective nutrition, which is the essential element of 

 the disease. 



The same characters, with but little variation, are 

 also indicative of the scrofulous habit in horses, sheep, 

 and swine. 1 



In the heredity of scrofula, it appears that the 

 constitutional defect is readily transmitted; but it 

 may present itself in a different form from that ob- 

 served in the generations immediately preceding. If 

 the lungs are affected in one generation, the inherited 

 predisposition of the next may consist in a tendency 

 to glandular swellings, mesenteric disease, or some 



1 Scrofula in its various forms may be developed in animals that 

 are not predisposed to it by inheritance. The most potent causes of 

 the disease in such animals are, -protracted disorder of the digestive 

 organs, food deficient in quality and quantity, impure water, confine- 

 ment in damp, filthy stables, that are not well ventilated nor lighted, 

 exposure to cold, or any other condition that lowers the vital powers. 

 The too common practice of crowding a large number of animals into 

 filthy compartments, that are not well ventilated, is undoubtedly an 

 efficient cause of the disease. According to Dr. Aitken, " the broadest 

 fact established regarding the exciting cause of scrofula is, that the 

 domesticated animal is more liable to scrofulous disease than the same 

 animal in the wild state. The stabled cow, the penned sheep, the tame 

 rabbit, the monkey, the caged lion, tiger, or elephant, are almost in- 

 variably cut off by scrofulous affections no doubt due to deficient 

 ventilation, and the abeyance of normal exercise of the pulmonary 

 function " (" Practice of Medicine," vol. i., p. 234). 



When the predisposition to scrofula is inherited, these conditions 

 will be intensified in their action as exciting causes of the disease. 

 Swine are said to be particularly liable to scrofulous affections, but this 

 is not surprising, as the too general violation of sanitary laws that pre- 

 vails in their management cannot fail to develop the disease, even in 

 cases where the system is not predisposed to it by inheritance. Some 

 of the most fatal epidemics among swine may be caused, in part at 

 least, by the development of scrofulous disease. 



