52 MALL. [Vor. XIX. 
there was some change in either of the germs before fertiliza- - 
tion took place. On the other hand, experimental work on 
amphibian, fish and bird embryos shows that monsters can be 
produced with ease from perfectly normal fertilized eggs. In 
general the methods employed by experimental teratologists 
is to subject the eggs to various insults which affect the nutri- 
tion and impair the growth of the embryo. If now a similar 
condition can be found to exist for human pathological ova 
which corresponds with those the experimental teratologist 
produces, the point is proved, that is, many merosomatous 
monsters may be formed by placing normal ova into an un- 
favorable environment. All of our experience in teratogeny, 
if read aright, indicates that the normal ovum got into a 
diseased uterus did not implant itself well, and the consequent 
impairment of nutrition produced a monstrous embryo. 
This hypothesis, which will be proved to be correct under 
the heading of tubal pregnancy, explains fully the presence of 
so many pathological embryos in multiple abortions and the 
apparent germinal origin of merosomatous terata like spina 
bifida and anencephaly. 
His,® in the discussion of normal and abnormal embryos, is 
rather of the opinion that pathological embryos are due to 
primary changes in the germ, and that their abortion naturally 
takes place because such ova act as foreign bodies in the 
uterus. In some instances, however, he excludes the possi- 
bility of the primary cause being due to an interference with 
their development, such as may be brought about by deficient 
nutrition, lack of oxygen and mechanical influences due to the 
uterus being displaced. Later,® in a discussion of open ques- 
tions in pathological embryology, he seems to be inclined to 
abandon the theory of the germinal origin of pathological ova 
altogether, for the examination of several specimens showed 
that the changes within them were of a secondary nature. 
They indicate that the embryo is in process of dying, that 
"His, Anatomie menschl. Embryonen, II, 1882. 
*His, Virchow Festschrift, I, 1899. 
