iv GENERAL CONSIDERATIONS OX THE TEXTURES. 



" organic systems" to designate the textures taken in this point of view, 

 and the term has been very generally employed by succeeding writers. 

 Of the tissues or organic systems enumerated, some are found iii nearly 

 every organ ; such is the case with the connective tissue, which serves as 

 a binding material to hold together the other tissues which go to form an 

 organ ; the vessels, which convey fluids for the nutrition of the other 

 textures, and the nerves, which establish a mutual dependence among 

 different organs, imparting to them sensibility, and governing their move- 

 ments. These were named by Bichat the "general systems." Others 

 again, as the cartilaginous and osseous, being confined to a limited num- 

 ber or to a particular class of organs, he named "particular systems." 

 Lastly, there are some tissues of such limited occurrence that it has 

 appeared more convenient to leave them out of the general enumeration 

 altogether, and to defer the consideration of them until the particular 

 organs in which they are found come to be treated of. Accordingly, the 

 tissues peculiar to the crystalline lens, the teeth, and some other parts, 

 though equally independent textures with those above enumerated, are for 

 the reason assigned not to be described in this part of the work. 



Structural Elements. It is further to be observed, that the tissues above 

 enumerated are by no means to be regarded as simple structural elements ; 

 on the contrary, many of them are complex in constitution, being made up 

 of several more simple tissues. The blood-vessels, for instance, are com- 

 posed of several coats of different structure, and some of these coats 

 consist of more than one tissue. They are properly rather organs than 

 textures, although they are here included with the latter in order that 

 their general structure and properties may be considered apart from their 

 local distribution ; but indeed it may be remarked, that the distinction 

 between textures and organs has not in general been strictly attended to 

 by anatomists. The same remark applies to mucous membrane and the 

 tissue of the glands, which structures, as commonly understood, are highly 

 complex. Were we to separate every tissue into the simplest parts which 

 possessed assignable form, we should resolve the whole into a very few 

 constructive elements; and, having regard to form merely, and not to 

 difference of chemical constitution, we might reduce these elements to the 

 following, viz. 1. simple fibre; 2. homogeneous membrane, either spread 

 out or forming the walls of tubes or cells ; and 3. globules or granules, 

 varying in diameter from the T T<roZ)* n to the ^ ~^th of an inch. These, 

 with a quantity of amorphous matter, homogeneous or molecular, might be 

 said, by their varied combinations, to make up the different kinds of 

 structure which we recognise in the tissues ; and if we take into account 

 that the chemical nature of these formative elements and of the amorphous 

 matter may vary, it will be readily conceived that extremely diversified 

 combinations may be produced. 



PHYSICAL PROPERTIES. 



The animal tissues like other forms of matter are endowed with various 

 physical properties, such as consistency, density, colour, and the like. Of 

 these the most interesting to the Physiologist is the property of imbibing 

 fluids, and of permitting fluids to pass through their substance, which 

 is essentially connected with some of the most important phenomena that 



