292 
GEORGE ARNOLD. 
from one cell to another (fig. 1, a, b, c) and passing evenly 
distributed through the periphery of each cell to the cir- 
cumjacent cell-surfaces. Even so, the course of the fibrils is 
limited mainly to the more central area of each surface of the 
epidermal cells, thereby leaving the corners free. 
It was very noticeable that at the margin of the tissue, 
where the penetration of the fixative was most thorough, the 
cell-margins rarely show the typical prickles to the presence 
of which is due the common histological name of these cells, 
i.e. prickle-cells. 
On the contrary, the cell-surfaces have exceedingly fine 
pittings and prominences, which in cross section present the 
aspect of a minutely serrated line (fig. 1, junction of cells 
b and c, b and d). In those portions of the tissue more 
remote from the immediate action of the fixative, this serrated 
margin is replaced entirely or in part by the tj^pical prickles. 
It is in such cells that the epidermal fibrils appear to pass 
from one cell to auother by protoplasmic bridges, formed by 
the junction at their apices of two opposing prickles (fig. 1, 
j), and fig. a1). 
I have observed this condition in epidermis on other 
occasions where the fixation has been insufficient, and there 
is a strong suggestion that the so-called prickles are artifacts 
produced by the unequal and faulty fixation. 
Epidermis is a notoriously difficult subject for fixation, the 
horny layer acting as a barrier to the rapid penetration of 
the fluid, and it is precisely among the cells immediately 
below the horny layer (rete mucosum) that prickles are most 
obvious. The passage of leucocytes and lymph corpuscles 
between the cells of the rete mucosum produce by pressure 
the formation of prickles, but the evidence brought forward 
above suggests that it is only a transient condition of the 
surface of the cells. 
As has been said, there are a few cells here and there in 
the tumour, in which the fibrils present a normal appearance, 
but in the vast majority the fibrils are in different stages 
of degeneration. 
