180 THE BREEDING OF ANIMALS 



are recorded among the domestic animals of supposed 

 cases of the heredity of pathological conditions. Among 

 the diseases which have been regarded as hereditary are 

 tuberculosis, melanosis, broken wind, specific ophthalmia, 

 blindness, spavin, ringbone, curb and many other diseases. 

 The discussion of the transmission of diseased conditions 

 of the organism brings forward again the entire question 

 of the possible inheritance of acquired characters. In 

 general it may be said that recent researches in biology 

 have resulted in demonstrating that many diseases which 

 were formerly regarded as transmissible are no longer 

 believed to be transmitted through inheritance. This 

 certainly applies to all diseases which are contracted 

 after birth. Some diseases which are the result of a 

 definite variation in the germ-plasm will of course be 

 transmitted. We must therefore clearly distinguish 

 between inborn disease and acquired disease. Certain 

 diseases or defects are undoubtedly transmitted from 

 parent to offspring. Whenever such defects represent 

 changes in the germ-plasm, then such defects will be as 

 certainly transmitted as any other character of the animal. 



Such defects which may be transmitted are deaf- 

 ness, color-blindness, idiocy and possibly rheumatism, 

 gout and insanity. In the latter diseases their apparent 

 transmissibility may be the result only of a predisposition. 



167. Acquired diseases. Many diseases of the do- 

 mestic animals are acquired after birth. A large number 

 of pathological diseases are due to infection. All such 

 diseases are no more certainly transmitted than are other 

 acquired characters. Tuberculosis is the result of infec- 

 tion by a specific germ and this germ may be acquired 

 under certain conditions by the animal organism. In 

 the case of bone diseases of horses, which were for a long 



