FLUIDS. 61 



other solid elements : Pigment, Fat, Cuticle, Horny textures, Epithe- 

 lium, Crystalline lens, Cartilage. 



3. Simple cells, or their contents, altered in form : Ciliated texture, 

 Spermatozoa. 



4. Compound cells, separate or mixed with other textures: Ovum, 

 Cranglionic corpuscles. 



II. Textures exhibiting a simply fibrous structure. 



1. Filamentous (areolar) texture ; formerly Cellular texture. 



2. Fibrous textures: Tendon, Ligament, Fibrous membranes, Fi- 

 brous plates. 



3. Elastic fibrous texture. 



III. Textures exhibiting a tubular structure. 



1. Containing moving fluids : Bloodvessels and Absorbent vessels. 



2. Containing muscular substance : Striated and non-striated mus- 

 cular fibre. 



3. Containing nervous matter : Primitive nerve tubes. 



IV. Textures exhibiting a membranous structure. 



1. Principally filamentous : Serous and Synovial membranes. 



2. Filamentous and vascular: Mucous membranes; True skin. 



3. Membrane and cells : G-lands. 



4. Membrane and Bloodvessels, &c. : Lungs. 



In combining to form the different structures, the solids are arranged 

 in various ways. Of these, the chief are in filaments or elementary 

 fibres, tissues, organs, apparatuses, and systems. A filament is the 

 elementary solid. A fibre consists of a' number of filaments united 

 together. Occasionally, this is called a tissue : the term tissue usually, 

 however, means a particular arrangement of fibres. An organ is a 

 compound of several tissues. An apparatus is an assemblage of organs, 

 concurring to the same end : the digestive apparatus consists of the 

 organs of mastication, insalivation, and deglutition, the stomach, duo- 

 denu]$r,' pancreas, liver, &c. These may be, and are, of very dissimilar 

 character, both as regards their structure and functions ; but, if they 

 concur in the same object, they form an apparatus. A system, on the 

 other hand, is an assemblage of organs, all of which possess the same 

 or an analogous structure. Thus, all the muscles of the body have a 

 common structure and function ; and form, in the aggregate, the 

 muscular system. All the vessels of the body, and all the nerves, for 

 like reasons, constitute, respectively, the vascular, and nervous sys- 

 tems. 



d. Of the Fluids of the Human Body. 



The positive quantity or proportion of the fluids in the human body 

 does not admit of appreciation, as it must vary at different periods, 

 and under different circumstances. The younger the animal, the greater 

 is its preponderance. When we first see the embryo, it appears to be 

 almost wholly fluid. As it becomes gradually developed, the proportion 

 of solid parts increases, until the adult age ; after which it becomes less 

 and less in the progress of life. During the whole of existence, too, 

 the quantity of fluids in the body fluctuates. At times, there is plethora 



