i44 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
increased greatly in intensity at what should have been a monthly period, and was 
accompanied by vomiting and a ' bearing down sensation.' There was no vaginal 
discharge. Abdominal section was performed on March 5th, 1901, and a large cyst, 
containing a thin clear fluid, was removed from the right side. At the operation it 
was noted that the uterus was wrinkled on its peritoneal surface, and equal in size to 
a four-and-a-half months' pregnancy. 
On March 24, after a week's slight preliminary bleeding the patient expelled 
a vesicular mole (see Fig. 6, Plate IX). 
That the existence of ovarian cystic disease is an important factor in the 
causation of vesicular mole has still to be proved, but as the two conditions have 
many points in common, it is probable that their occurrence indicates something 
more than a coincidence. Until, however, a greater number of cases are investi- 
gated with special reference to this point, the question must remain undecided. 
Another fact, which must not be overlooked, is that a neurotic temperament 
frequently obtains in persons who are the subjects of this disease, and a history is 
often given in these cases of mental worry and distress, leading to much depression 
and general weakness. This may be regarded as an important predisposing factor. 
As a primary cause, the circulation of a toxine in the maternal blood has been 
suggested, developed during gestation, and determining by its irritative qualities, 
degeneration of the chorionic villi. This, we believe, comes nearer the truth than 
any of the foregoing theories, but it is, in the present state of our knowledge, 
impossible to definitely prove it. 
Frequency. The approximate frequency has been estimated at 1 in 20,000 
pregnancies, but as will be readily understood, the estimate is liable to wide variations, 
owing to the difficulty in collecting such statistics, and the fact that many cases 
occurring in the early months of pregnancy are diagnosed as carneous moles and 
recorded merely as abortions. 
Symptoms. These, stated briefly, are enlargement of the uterus, haemorrhage 
or amenorrhoea, a watery blood-stained discharge, occasionally containing vesicles, 
and the usual symptoms indicative of pregnancy. 
In all the cases I have collected, the only constant symptom was enlargement 
of the uterus, but it is important to note that enlargement beyond what is expected 
from the period of gestation does not by any means occur in all cases, as so 
many writers of the text books would have us infer. 
Out of seven cases, in one only was the uterus larger than the corresponding 
period of pregnancy ; in all the others, the uterus was considerably smaller. In two 
cases, where the period of pregnancy was eight months, the uterus only corresponded 
in size to a four-and-a-half months' pregnancy ; in another, a nine-and-a-half months' 
history to a six months' uterus, etc. This latter case is of special interest, as it 
represents one of the few cases in which a molar pregnancy lasted beyond the full term. 
