12 
Ww: 
INTRODUCTION. 
boiling leaves it unchanged, by concentrated sulphuric acid 
it is dissolved gradually, by alkalis readily. Scales, nails, 
&c., which consist of this tissue, are secreted by a highly 
vascular bed (matrix) in layers. The Epithelium is formed 
in part, like the Epidermis, of flat cells: in other situations 
these cells are cylindrical, or conical, and stand perpen- 
dicularly, side by side, like fibres. In many situations (as 
the nasal cavities, the respiratory organs of mammalia, birds 
and reptiles, the gills of bivalve molluscs) these conical cells 
carry cilia, whose motions had been seen on the surface of 
the body of many of the lower animals by the earlier 
observers, but were distinctly recognised by PurkrnsE and 
VALENTIN as a very general phenomenon of the animal 
kingdom only a few years ago. 
Cartilaginous Tissue (tela cartilaginea) is semi-transparent, 
elastic, and mostly of a bluish-white colour. On section it 
presents a very smooth surface and looks like a substance of 
uniform density. But under the microscope, small, granular, 
round or oblong corpuscles are seen in the clearer trans- 
parent principal mass. The glue which is obtained from 
cartilage by boiling differs in many respects from the glue 
of bone, and was called by MurLurr, who first called atten- 
tion to the difference, Chondrine (cartilage-glue). This glue 
is also obtained from the cornea of the eye, which is com- 
posed of many thin layers or plates formed of fibres that 
cross one another in all directions. Certain yellow highly 
flexible and elastic cartilages contain numerous fibres (carti- 
lagines fibrose): to this division belongs ew. gr. the cartilage 
of the external ear in man and mammalia. Cartilage con- 
tajps two-thirds of its weight of water. In the ash are 
found carb. soda, sulph. soda, and carb. lime as the chief 
constituents. Here belongs: 
Osseous Tissue (tela ossea). The tissue of bone is hard 
and opaque, and of a laminated structure. The chief con- 
stituents are cartilage, which on boiling passes entirely imto 
gelatin or common glue: and bone-earth, of which the 
quantity increases with the age. The last consists princi- 
pally of phosphate of lime, which has a great affinity with 
the colouring matter of madder, so that the bones of animals 
