A CLASSIFICATION OF THE ANIMAL TISSUES. 367 



A CLASSIFICATION OF THE ANIMAL TISSUES. 



Professor Schwann's classification of the fundamental tissues of the 

 human body is that generally adopted, more than half of which tissues 

 are formed out of the cellular or simple membranes. 



1. Simple membrane : employed alone I Examples : Walls of cells, capsule of 



in the formation of compound y lens of the eye, sarcolemma of muscle, 



membranes | &o. 



1 Examples : White and yellow fibrous 



2. Fibrous tissues .... I tissue, areolar tissue, elastic tissue, 



J &o. 



3. Cellular tissues .... 1 Examples : CartUage, fat, pigment, 



J gr^ey nervous matter, &c. 



4. Sclerous or hard tissues ... 1 Examples: Rudimentary skeleton of in- 



J vertebrata, bone, teeth, &o. 



5. Compound membranes : composed of ~ 



simple membrane and a layer of 

 cells of various forms (epithelium 

 or epidermis), or of areolar tissue 

 and epithelium 



6. Compound tissues ; a, those com- T 



posed of tubes of homogeneous I 



membrane, containing a peculiar f Examples : Muscle, nerve. 



substance J 



Examples ; Mucous membrane, skin, 

 true or secreting glands, serous and 

 synovial membranes. 



I, those composed of white fibrous 1 _ , „., 



tissues and cartilage . . . | Example : Fibro-cartJage. 



Cellular Membrane, or Tissice. — Cellular or areolar tissue is gene- 

 rally distributed throughout the body, and various forms of this cell- 

 fibre are found ; it is seen uniting together component parts, filling up 

 interstices between them, and affording a support to the blood-vessels 

 and nerves, before they are distributed to the various organs. This 

 fibre is soft, clear, smooth, and extremely minute, being the l-12,000th 

 of an inch in diameter, sometimes less. The fibre is usually found 

 united together in bundles, the l-2000th of an inch broad : if these 

 be acted upon by dilute acetic acid they swell up, become transparent, 

 and the appearance of fibrous structure is no longer seen, although 

 some fibres that were not previously observed may become more dis- 

 tinct. The first kind does not refract the light strongly ; the second 

 kind does, showing some chemical difierence in their composition. 



Cellular tissue, if dried, becomes a yellowish, brittle, transparent 

 mass ; but regains its former state if placed in water. The fibres have 

 a remarkable arrangement and disposition. They are often deposited 

 in a spiral manner. At other times they are regularly undulating. In 

 fibres taken from some parts of the body, we find that a fasciculus is 



