538 
GENETICS: DAVENPORT AND CONARD 
fractures. The tendency is often outgrown after puberty. Lovett 
and Nichols^ have shown that in osteopsathyrosis the periosteal bone form- 
ation especially is imperfect, since the Haversian systems are not formed. 
An examination of a large number of family histories shows clearly 
that heredity in osteopsathyrosis is t3^ically direct — i.e., the factor that 
determines the irregular bone formation is a dominant one. The view 
that it is due to ''some disturbance of metabolism of the mother" is 
disproved by the instance of twins, described by Schwarz and Bass,^ 
one of whom showed osteopsathyrosis at birth while the other did not. 
The rare exceptions to the rule that a generation is not skipped are 
explained by the well known principle of imperfection of dominance or 
possibly to a lack of knowledge of an infantile condition of a parent. 
An association of osteopsathyrosis with blue sclerotics has often been 
pointed out. The condition of blue sclerotics also appears to be a domi- 
nant trait. It is barely possible that the association is not a necessary 
one but on the other hand, there may be a linkage between these traits; 
pedigrees are not yet extensive and numerous enough to decide. 
That osteopsathyrosis depends upon a single dominant factor is further 
indicated by the fact that the proportion of children in an affected fra- 
ternity that shows osteopsathyrosis is approximately half — actually 55%. 
The presence of biotypes of osteopsathyrosis can be recognized. 
In some famiHes the sHghtest pressure results in fracture; in other families 
the bones are fairly resistant. The commonest bone to break is the 
femur. But in some families the humerus seems especially weak and in 
still others the clavicle is frequently broken. Thus, associated with the 
imperfect bone development are special family traits that modify the 
result. 
It appears, to summarize, that of a parent who was in early Hfe osteop- 
sathyrotic at least half of the children will be similarly affected. But 
if neither parent, though of affected stock, has shown the tendency then 
expectation is that none of the children will have brittle bones. More- 
over, when a parent is affected it is possible that his children will show 
the tendency at about the same time of life, in the same bones and to the 
same degree as he himself showed it. 
The full paper with numerous pedigree charts will appear in the Bulle- 
tin of the Eugenics Record Ofhce. 
' Lovett, R. W. and Nichols, E. H., Brit. Med. London, 1906, II, 915. 
2 Schwarz and Bass, Medical Record, 1912, p. 317. 
