THE 



GENERAL ANATOMY OF THE TISSUES. 



I. OF THE ELEMENTARY PARTS. 



§ 4. If the solid and fluid constituents of the human body be examined 

 with the aid of strong magnifying powers, it appears at once that the 

 smallest parts which they exhibit to the naked eye, as granules, fibres, 

 tubes, membranes, &c., are not the ultimate elements in respect of form, 

 but on the contrary, that all, in conjunction with a universally distri- 

 buted, fluid, semi-fluid, or even solid, homogeneous, uniting substance, 

 contain minute particles which differ in different organs but in the 

 same organs have always a similar appearance. There are various 

 kinds of these so-called elementary parts, simple and compound. The 

 simplest are quite homogeneous, without any trace of their being com- 

 posed of heterogeneous portions and are nearly allied to the inorganic 

 forms, the crystalline granules and crystals, which also occur in the 

 animal organism. Others already show that they have suffered a diffe- 

 rentiation into an investment and determinate, though homogeneous 

 contents : in others again, the contents present differences. The most 

 important among all these forms, which may be comprehended under 

 the general title of ''^simple elementary parts,'' are the cells, which not 

 only form the starting-point of every animal and vegetable organism, but 

 also, either as cells or after having undergone manifold metamorphoses, 

 make Up the body of the perfect animal, and in the simplest animal 

 and vegetable formations (unicellular animals and plants), even enjoy 

 an independent existence. Compared with cells, all other simple ele- 

 mentary parts have quite a subordinate importance, so far as their direct 

 participation in the formation of the tissues and organs is concerned ; 

 while, from their being almost all contained in the interior of cells and 

 from their being concerned in many and most important ways in the 

 vital processes of these cells, their importance in other respects is very 

 great. 



The simple elementary parts, which at first wholly comprise the com- 

 mencing animal (or plant), often unite in the course of development in 



