STRUCTURE OF THE HUMAN BODY. 27 



be produced, is termed the cellular. It is this which I have 

 already alluded to as entering into the compositions of every 

 organ, and forming the basis of the solid structure of the 

 body. Into its cells all other kinds of animal matter are de- 

 posited as phosphate of lime and gelatine, which form the bones. 

 It forms sheaths for the muscles and nerves ; composes a great- 

 er part of the ligaments, tendons, and cartilages, and even the 

 hair and nails, thus constituting not only the basis of all the 

 solids, but serving as a bond of union by which the organs 

 are connected together. By its softness and elasticity, and 

 the oily fluid by which its cells are filled, it also promotes 

 the mobility of the parts on one another. It possesses the 

 property of contractility, and is composed chiefly of gelatine. 

 9. One remarkable circumstance connected with this tis- 

 sue is, that as it exists throughout the body, it forms a con- 

 nected whole, or an immense net-work, every where accessi- 

 ble to air. This is shown by forcing air into its cells, in 

 any part of the body ; which is found gradually to penetrate 

 and pervade every part till the whole body is inflated. 

 Butchers often avail themselves of a knowledge of this fact, 

 by blowing their meat, or in other words, inflating animals 

 by making a puncture in some part where the cellular tissue 

 is loose, and from this one aperture forcing the air to the 

 most distant parts of the body, in order to give the meat a 

 fat appearance. If we raise up a portion of cellular mem- 

 brane, in the form of a thin slice, it appears as a semi-trans- 

 parent and colourless substance, composed of minute threads 

 which are seen to cross each other in every possible direction, 

 leaving spaces between them, and thus forming a mesh, 

 similar to the spider's web. As to the precise form of these 

 cells or cavities we have no accurate knowledge. They are 

 generally supposed to be narrow spans with acute angles, the 

 sides of which are flattened, and when not forcibly expanded, 

 we may suppose to be in contact. Some physiologists in- 

 deed deny that any cavities at all exist, but the weight of 

 evidence is altogether in favour of their existence. 



