No. 1.] ORIGIN OF HUMAN MONSTERS. 33 
and not constructive processes are present in parts of the 
embryo which are becoming deformed. As this question is 
being investigated more and more it is clear that we must 
build up a pathology of our own based upon observations 
upon normal healing of wounds,’ etc., in embryos, just as 
Morgan was compelled to study anew the development of the 
frog in order to interpret properly the various malformed 
eges he had under consideration. 
I am quite certain that in the human embryo the cells may 
spread from the blood-vessels into the surrounding tissues 
after the heart has stopped, and I am also certain that mesen- 
chyme cells may separate and segregate, and that the cells of 
the central nervous system may become necrotic in part, dis- 
solve their connections and gradually fill the central canal. 
It matters little what we call this process, it probably includes 
a series of processes, but for the present I shall apply to it 
the term dissociation. In doing this I do not commit myself 
as to the origin of a group of cells. In order to describe my 
human embryos properly I must also use the term macera- 
tion, and by it I mean that the process has taken place after 
the death of the part. When cells dissociate they are still 
alive, but they are on the way to meet their fate. As the 
tissues continue to grow their sharp, borders are broken and 
they gradually become hopelessly confused. For the present 
the terms dissociation and maceration will do; in a short 
time it will be necessary to displace them, for experimental 
teratology will continue to be a fruitful field of research. 
Sopium Monsters—SPpiInA BIFIDA AND ANENCEPHALY. 
Probably the most satisfactory chapter at present in experi- 
mental teratology is the subject of spina bifida. Under this 
heading, of course, is meant that kind of spina bifida which 
is due to a lack of closure of the neural canal and not the 
kind that may be produced in older embryos after the cord is 
"See, for instance, Eycleshymer, Amer. Jour. Anat., VII, 1907. 
