38 MALL. [Vov. XIX. 
the whole nervous system is thrown out by means of acetone- 
chloroform. The animals remain perfectly motionless and 
also develop dropsy, due probably to the effect of the acetone 
upon the heart of the animal. As I have mentioned above, . 
Knower has shown that simple enucleation of the heart 
anlage causes an embryo to grow without a heart, which 
always has more or less dropsy, especially of the pronephros, 
while those in which the nervous system only has been re- 
moved are not thus affected. Therefore, when the nervous 
system is paralyzed by the action of acetone, which also 
retards the action of the heart, we must conclude that the 
dropsy of the embryo is due to the deranged heart and not 
to the damaged nervous system. 
In their experiments, Panum and Dareste occasionally ob- 
tained spina bifida in chicks, not including those monsters in 
which the brain was deformed. Some time later Richter® 
found three cases of spina bifida among several hundred hens’ 
eggs upon which he experimented. Otherwise these chicks 
were quite normal and no amniotic bands were found. This 
last point was considered to be of great importance, but now, 
since monsters are produced in animals without an amnion, 
it would be well, it seems to me, to relegate the amniotic theory 
of the production of monsters into the class into which that of 
maternal impressions has fallen. In Richter’s cases, how- 
ever, the spina bifida was more or less associated with anen- 
cephaly, and there were also specimens of exencephaly as well 
as a few of spina bifida occulta. In other words, the condi- 
tions here were more complicated than those found in the 
frog. 
In my own specimens of human embryos there are at 
least twelve good ones of spina bifida. These are among 
163 pathological ova, or about one case of spina bifida in 
every 200 pregnancies. Acording to Panum’s table, there 
were 38 specimens of spina bifida among 404 monsters, or 
again about Io per cent. If one monster results from every 
*Richter, Anat. Anz., III, 1888. 
