54 MALL. [Vou. XIX. 
appears to be normal all kinds of secondary changes have 
taken place. The mesodern is fibrous, hyaline or cedematous, 
the villi are atrophic, hypertrophic or missing altogether, and 
the syncytium is irregular or necrotic, and sometimes it has at- 
tacked and invaded the mesoderm of the chorion. The decidua 
when present is usually infiltrated with leucocytes, which often 
accumulate in great masses, or often form abscesses. All this 
could take place if the embryo had died and the ovum had 
continued to grow, but on account of the presence of a dead 
embryo the uterus reacts as if it had a foreign body to expel. 
In fact, most of these changes just enumerated probably took 
place long after the embryo had become monstrous, and we 
are no doubt treating with the primary process, much intensi- 
fied by the presence of a pathological ovum. The final proof 
in favor of the theory that these changes are primary will be 
given under the discussion of tubal pregnancy. 
It will be noticed that the “normal” chorion is most com- 
mon in young ova, that is, before the process of destruction 
has been under way for a long time. In an earlier publica- 
tion? upon this subject I was much inclined to the idea that 
the primary difficulty in a pathological ovum is to be sought 
in the embryo, but later’? I formed the specimens into two 
groups: (1) Those in which the primary cause lies in the 
embryo, and (2) those in which it is outside of the chorion. 
This gradual change of my ideas is identical with that which 
both His and Giacomini passed through, for all of us based 
our conclusions upon a simple morphological study. The 
morphologist must be very careful in the arrangement of his 
sequences, and I think it is to our credit that we have been 
so. But now, since we have experimental teratology and a 
more careful study of the gynecological history of the speci- 
mens to fall back upon, it seems to me that the solution of 
the problem is at hand. 
The ova which appear to be normal, but have within them 
deformed embryos, or none at all, are the ones that require 
*Mall, Welch Festschrift, J. H. Hosp. Rep., IX, 1900. 
*Mall, Vaughan Festschrift, Ann Arbor, 1903. 
