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 

 peculiarity 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- 



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tor^Tit) tab 



j coiisins I 1 



01 



iN 



cou 



sins 



71 8 I 

 I nerve and 

 lung trouble' 



w 



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

 even from unaffected parents; hence due to a defect. Bernhardt, 18S5. 



sponsiveness in the voluntary 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 Herringhara 

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



