ITS STRUCTr:RE AND FUNCTIONS, 259 



there is Muscular Tissue, Nervous Tissue, C'onnective Tissue, and 

 others, all working together for the common good of the organism. 

 The advantages of this division of labour and co-operation is very 

 great, and quite self-evident, as it enables things to be accomplished 

 which, in a unicellular organism, could not be attempted. 



It is only with two of these departments or tissues, or, rather, 

 with part of two, whose work is combined and blended together, 

 that I propose to deal to-night: — ist. The Epithelial Tissue, or 

 Epithelium ; and 2nd, the Connective Tissue, the layers of which 

 form the skin. Of course, we must bear in mind that in discussing 

 any individual department of a large establishment, we cannot 

 isolate it entirely from the rest, but shall have to frequently con- 

 sider its relation to other departments, such as, in this case, the 

 Blood, Muscular Tissue, and especially the Central Nervous 

 System. 



The skin consists of a mass of cells arranged in two distinct 

 layers: — A, More superficial — Epidermis; B, Deeper — Cutis Vera, 

 Dermis, or Corium. The former is epithelial, the latter is con- 

 nective-tissue, which, in various conditions, e.g., fibrous, cartilagi- 

 nous, and bony, forms the framework of the body. 



The upper or epithelial portion consists of several superimposed 

 layers of cells lying close together, with intercellular substance 

 joining them, and arranged much like bricks in a wall. The cells 

 vary in shape from the lower layers upwards ; thus, the deepest 

 layers of all are somewhat cubical in shape, whilst as the higher 

 layers are reached they become more and more flattened and scale- 

 like. The lowest layer is very uneven, as it has to fit over the 

 dermis or true skin underneath, which, as we shall see, is constantly 

 rising into little projections or papillae. 



The cells of the different layers or strata also differ in their 

 chemical composition ; the deepest stratum consists of cells whose 

 composition approaches that of ordinary living protoplasm, whereas 

 the superficial strata become horny in character, so much so that, 

 in parts where there is much pressure, such as the palms of the 

 hands and soles of the feet, this horny layer is much developed ; 

 a condition well seen in the hands of those occupied in various 

 Sheffield trades, e.g., those who do much filing, and many others. 



This difference in chemical composition causes also a difference 



