14 RICHARD ASSHETON AND THOMAS G. STEVENS. 
They can be found only sparingly distributed in region A, 
not at all in region C, but abundantly in region B. Here 
they may be found in the fibrous tissues of the foetal villi, and 
occasionally in the foetal blood in leucocytes. They occur 
chiefly, however, in the syncytial layer, which is crowded 
with them, especially around the nuclei (fig. 11), and in the 
leucocytes in the maternal blood (figs. 13 and 14) and in the 
leucocytes in the lymphatic spaces in the large trunks of the 
foetal villi. The leucocytes of the maternal blood are nearly 
always loaded with this pigment. 
We find that the pigment is free of iron. When sections 
are treated with ferro-cyanide of potassium and dilute hydro- 
chloric acid, there is a general blue coloration after a while, 
the blood-corpuscles and certain parts of the fcetal fibrous 
tissue being particularly strongly stained. The pigment 
granules are absolutely untouched by the blue. They are in- 
soluble in ether and alcohol and soluble in caustic potash 
1 per cent., and in ammonium sulphide. 
There are several points of interest in connection with this 
pigment, which may be considered to be an excretory pro- 
duct. Fig. 13 is a drawing of a part of a maternal channel 
lying close against a feetal villus. ‘The syncytial layer is 
attached chiefly to the latter, but parts are adherent to the 
maternal channel wall. ‘he maternal channel contains red 
corpuscles of different sizes, and large leucocytes, which are 
loaded with pigment, some sticking to the walls, others free 
within the blood-stream and some (/!) apparently undergoing 
disintegration, the pigment being set free in the stream. 
Frequently these cells may be found flattened up against the 
walls, as in fig. 14 (end) and, indeed, sometimes it is difficult 
to say whether they do not penetrate the walls. 
Again, it is possible to find all stages between flattened 
pigment-laden cells as (J) in fig. 14 and (end) of the same 
drawing, which are not to be distinguished from the cells we 
find in other parts of the channels, and have spoken of as 
possibly endothelial. 
It is likely that the leucocytes play some part in the trans- 
