198 M. F. GUYER AND E. A. SMITH 
12 living young were obtained, and from others treated with 
serum sensitized to rabbit testis, 36 were secured, or a total of 
48 young which survived long enough to show the condition of 
their eyes. In not a single one of these 48 controls was there 
evidence of eye defect. As far as our experiments go, therefore, 
the interpretation is that the effect of the lens-sensitized serum is 
specific. 
As to why the lenses of the mothers into which the lens-sensi- 
tized serum was originally injected were not attacked, we have 
no further explanation to offer than the suggestion in our earlier 
paper that the lack of circulation of blood through the lenses of 
adults prevents the sensitized serum from reaching them in suf- 
ficient quantity to produce visible change. In the fetus the con- 
dition is very different. There, after the tenth day of develop- 
ment, the lens capsule is highly vascular, receiving blood from 
a specially developed branch (hyaloid artery) of the retinal ar- 
tery. This hyaloid artery, together with its plexus of blood- 
vessels surrounding the lens, normally disappears shortly before 
birth. 
PLACENTAL PENETRATION 
Yet another problem that requires attention is that of how the 
lens antibodies penetrate the placenta. From the study of F. 
R. Lillie (17) on the free-martin, it appears that in the case of 
two-sexed twins in cattle if the sex hormones of the male circulate 
in the female, the latter is transformed into a sterile free-martin. 
This happens only when secondary fusions of the chorions of the 
two individuals occurs, permitting direct anastomosis of the fetal 
circulation so that the blood of each may flow through the veins of 
the other. By implication therefore, without this direct connec- 
tion of blood-vessels the sex hormones of the male would presum- 
ably not reach the blood of the female fetus. It seems reason- 
able to suppose that as regards penetration of the placenta, sex 
hormones and ordinary antibodies or cytolysins would come in 
the same category. This may or may not be true. But it is 
possible that under normal conditions small quantities of sex 
hormones from the male do reach the blood of the female in the 
