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GEOllGE ARNOLD. 
the point where they lie at the apices of two opposing 
prickles. The other fibrils — “ longs filaments” — are much 
longer and thinner than the former ; they have no central 
nodule, and may be so long as to pass through more than two 
cells. Ranvier considered that these long fibrils represent 
the nodular fibrils in a stretclied-out condition, occasioned by 
the tension due to the passage of leucocytes through the 
spaces between the prickles, the nodular centre being of an 
elastic nature to facilitate such strains. And he attributes to 
these connecting fibres the difficulty of isolating the epidermal 
cells by maceration and other methods. 
Waldeyer (1882) and Lwoff (1882) described similar fibres 
which they found in the epidermal layer of the cortex of the 
feathers of birds. 
These observations apparently did not attract much atten- 
tion, and it is due to the work of Herxheimer (1889) that the 
interest of histologists was focussed on to these structures. 
Nevertheless, beyond indicating new methods of fixation 
and staining, Herxheimer had very little to add to the 
observations of the earlier observers. It is to be remarked 
that he called attention to the fact, noticed by subsequent 
observers, that these fibrils are more easily demonstrable in 
the cells of tumours and warts, and in the apparently healthy 
epidermal cells immediately adjacent to the growths. In a 
later paper (1899) he expressed the view that the fibrils are 
derived from the substance which forms the walls of the 
cytoplasmic alveoli. 
Kromayer (1892) described the protoplasmic fibrils in the 
epidermis of the palm and sole, and also in epitheliomata. 
He traced the course of the fibrils from one cell to another 
through the prickles. His observations agree with those of 
Ranvier and Herxheimer in that he showed that the fibrils 
are most strongly developed in the lowest layers of the rete 
mucosum,and are absent from the uppermost layers, in which 
the cytoplasm contains keratohyalin. The latter substance 
he derived from the fibrils themselves. 
In the lowest layer of the rete mucosum, i. e. the columnar 
