io8 HEREDITY AND EUGENICS 



there is no separation of hereditary and acquired 

 cases. 



Myoclonus - epilepsy, marked by (degenerative) 

 spasms of various muscles, is also a disease transmitted 

 as a homogeneous recessive character. One of the most 

 complete of family studies is that of Lundborg (191 3) 

 on a farmer family in Southern Sweden having this 

 affliction. Among the 2,232 individuals examined 

 he groups (i) 11 families as DDxRR, with 166 

 children all normal; (2) 11 families DRxDR, with 

 93 children, of which jy reached an age of over 

 15 years. Of these, 24, or 31-2 per cent., were 

 abnormal. Applying the statistical correction of 

 Weinberg gives 21-8 per cent, abnormal where the 

 expectation is 25 per cent. (3) DRxRR, 5 families 

 with 46 children, of which 40 reached over 15 3^ears 

 of age. Twenty of these were normal, or 45-3 per 

 cent, with the statistical correction. This is the only 

 Swedish family known to have the peculiarity, and 

 the results are in very good agreement with Men- 

 delian expectation. 



A condition which is said to be rare is hereditary 

 tremor. Bergman (1920) states that fifty families 

 showing this condition are mentioned in the literature. 

 It consists in rapid involuntary and rhythmic con- 

 tractions of certain groups of muscles. Usually the 

 arms and hands are affected, but sometimes also the 

 head or legs or the whole body. Hereditary tremor 

 most frequently appears in early youth, and often 

 increases in intensity later. It generally ceases during 

 sleep and perfect rest. Sometimes it appears only 

 in connection with exertions or emotions. The 

 tremor ma}^ be rapid (8 to 10 vibrations per second), 

 or slower (3 to 4 per second). People with hereditary 

 tremor are often nervous and emotionall}- unstable. 

 The handwTiting is affected, and may be almost 

 or quite illegible. Bergman traces this condition 



