116 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
amount of deposition of melanin in the cells. The figure 
represents a thin part of the section, where the cells are 
relatively widely separated, and where the pigment is less 
dense than usual. Although little can be seen in such 
sections it is evident that we have to deal with elongated 
cells loaded with masses of melanin. The latter is 
deposited in the form of fine granules, which are indivi- 
dually of a brown colour, but are dense black in mass. 
They are so closely aggregated that, asa rule, the pigment 
accumulations appear to be uniform in structure. At the 
edges of these masses, and in places where the deposition 
of the pigment is only beginning, the separate round 
granules can easily be seen. Although the study of such 
sections alone would, I think, be insufficient for the 
diagnosis of the growth, the appearance presented by 
them is strikingly similar to that of the illustrations of 
some human sarcomata. 
Fig. 2, Pl. V, represents part of a similar section to 
that described above, but the sections, after being mounted 
on the slides, were placed in commercial hydrogen 
peroxide for about 48 hours. The result is that the 
melanin is oxidised, and has assumed a light brown colour, 
and has become very transparent. Subsequent staining is, 
however, difficult, since the products of oxidation of the 
melanin still remain in the cells. But the spindle-shaped 
cells can now be clearly recognised. The latter are of 
very various sizes, and the largest that I measured was 
about 0°07 mm. in length. They are round in transverse 
section; usually swollen at the middle, no doubt because 
of the accumulation of the pigment there; and they taper 
at both ends and sometimes end in fine fibres. In many 
cases no nuclei can be seen in these cells, but this may be 
attributed to the difficulty of staining after the bleaching 
process. In other cases the nucleus has the appearance of 
