i6o THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
stain more accurately. There is no sharp line of demarcation between the healthy 
tissues and the invading cells, though it would appear from the uniform thickness of 
the muscular wall that the process of infiltration was proceeding with uniform 
rapidity. Masses of cells are seen making their way in between the muscular fibres, 
and at this point the involvement of the maternal blood vessels is seen. As shewn 
in the illustration, the cells approach the wall, penetrate into the lumen of the blood 
vessel, thence to be carried by the blood stream to some distant part of the body. 
Sections of the secondary deposits in the lung shew precisely the same 
structures as those found in the uterine tumour, so that it is unnecessary to recapitulate 
the description. It is, however, noticed that the nodule is more necrotic, the central 
part being composed almost entirely of blood clot and disintegrating tumour masses, 
s ) that the typical syncytial strands and the oval cells are seen most abundantly at 
the periphery, where they form a kind of investing membrane. The cells may be 
traced penetrating into the haemorrhagic area, either as fine strands, or as broader 
flattened masses. 
The protoplasm of the syncytium is more vacuolated than that of the primary 
tissue, and it appears in places .as though these vacuoles had been formed by the 
dropping out or absorption of a nucleus. Intense leucocytic exudation is here also 
a marked feature. 
In the immediate neighbourhood of the nodules, the lung tissue is seen to be 
in a state of congestion. The alveoli are choked with exudation, and the walls are 
thickened and inflamed. A bronchus close by also shews inflammatory changes, with 
secretion of mucus. 
From the consideration of these two cases, which, although differing some- 
what as regards the clinical course, agree in that the pathological elements found in 
each are identical, it is argued that this condition is one of true carcinoma, arising in 
the chorionic epithelium, and parasitic on the maternal organism. 
As shewn in the earlier part of this paper, the epithelium covering a villus is 
a strictly foetal structure, being the remains of the trophoblast, and further, that 
according to their position relative to the villus and the maternal blood, the cells 
assume either a flattened plasmodial form, the syncytium, or retain their primary 
cubical or polyhedral shape, the so-called zellschicht of Langhans. 
Taking this view, the difficulty experienced by so many observers, in assigning 
a separate origin for the two varieties of cells found in this condition, vanishes. It is 
evident that, as in the early villus, the pressure of the blood, and possibly some chemi- 
cal action of its plasma, can convert the polygonal cells of the trophoblast into a flat- 
tened condensed mass of syncytium, so, later in its history, the blood laden with some 
toxic element, can so act on the chorionic epithelium undergoing malignant prolifera- 
tion, as to cause condensation and formation of syncytial masses in precisely the same 
way. 
