i 4 2 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
PART II 
The chorionic vesicle is, in all stages of its existence, liable to undergo hyda- 
tidirorm degeneration (Fig. 5, Plate IX). This condition, about which so little is 
known, is of great interest, owing to the striking connexion it has been seen to 
oossess with chorion carcinoma, and as an understanding of the clinical features is 
essential to the true interpretation of the pathological appearances, a few cases, which, 
through the kindness of Professor Briggs, of the University of Liverpool, have come 
under my observation, will be discussed. 
According to the date of pregnancy at which the disease appears, the chorion 
may be affected. 
1. In its whole extent, in which case the mole presents an ovoid shape, 
corresponding closely with the interior of the uterine cavity, composed of vesicles 
varying greatly in size, having no trace of a foetus or amniotic cavity. 
It may or may not have an enveloping membrane of decidua. These cases 
originate in the early weeks of pregnancy, and form the commonest variety of the 
disease. 
2. In an area corresponding to what should have been the placenta. In 
these cases the mole is more compact ; there may be the remains of a foetus inside a 
well-defined amniotic cavity. This class arises during the first and second months of 
pregnancy. 
3. In a limited area of what appears otherwise as a normal placenta. Here 
the foetus may be quite healthy and well developed, the pregnancy having gone on 
to full term without an untoward symptom occurring. This class of cases is extremely 
rare, as are also those cases in which a twin pregnancy exists, one ovum being a living 
child and the other a vesicular mole. The literature bearing on these cases is very 
scanty, and, beyond the fact of their occurrence being recorded, little more is known 
of their pathology. 
The etiology of this condition is obscure, and many factors must be taken 
into consideration in trying to arrive at the true cause of the disease. 
The age of the patient is apparently of little importance, as the disease may 
occur at any time during the child-bearing period, cases having been recorded as 
early as seventeen and as late as fifty-three. It has, however, been noted that the 
condition is more frequent in multiparae, especially in those who have borne few 
children, and in those cases where the pregnancies have not followed each other with 
great rapidity. 
Although most writers agree in assigning as a predisposing cause, some 
pathological state of the mother, some have suggested syphilis in the father as a 
possible cause. 
