12 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 PURKINJE and 

 VALENTIN as a very general phenomenon of the animal 

 kingdom only a few years ago. 



VI. 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 MUELLER, 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 fibrosce}'. to this division belongs ex. gr. the cartilage 

 of the external ear in man and mammalia. Cartilage con- 

 tains 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 into 

 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 



