THE INHERITANCE OF FAMILY TRAITS 149 



32. Diseases of the Muscular System 



Since most muscular response is controlled by the nervous 

 system it is frequently difficult to determine whether a 

 pecuUarity of muscular response is due chiefly to the one 

 organ or the other. The classification of these diseases is 

 therefore somewhat arbitrary. 



a. Thomsen's Disease is a rather rare one in most local- 

 ities. It is characterized by lack of tone and prompt re- 



71 8. . 

 nerve and 

 lungtrouble^ 



Fig. 124. — Pedigree of Thomsen's disease. Appears in cousin marriagea 

 even from unafifected parents; hence due to a defect. Bernhardt, 1885. 



sponsiveness in the volmitary muscles. A striking pedigree 

 has been recorded by Thomsen (Fig. 124). It shows a re- 

 markable reappearance of the disease in the offspring of 

 cousin marriages and this indicates that the disease is due 

 to some sort of a defect whose nature has yet to be elucidated. 

 The clear eugenic advice is outmarriage. 



b. Certain Muscular Atrophies appear to be secondary to 

 diseases of the nervous system while others seem to originate 

 in the muscles themselves, without corresponding defects in 

 the nervous centers. In a family described by Herringham 

 (1885) sometimes all appendages, sometimes the arms only, 



