GENERAL HISTOLOGY. 



I— OF THE ELEMENTARY PARTS. 



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

 examined with the aid of magnifying- powers, it is seen that 

 the smallest elements of them visible to the naked eye, such as 

 granules, fibres, tubes, membranes, are not the ultimate, morpho- 

 ogical constituents, but that all contain, besides a generally distri- 

 buted, perfectly fluid or pulpy, or even solid, homogeneous con- 

 necting substance, other small particles which are different in differ- 

 ent organs and similar in similar ones. These elementary parts, as 

 they are called, are of manifold kinds, some more simple, others 

 compound. The most simple are perfectly homogeneous, without 

 indicating a trace of being composed of heterogeneous particles, 

 and are closely allied to the inorganic forms, the crystalline granules 

 and crystals, which likewise occur in animal organisms. Others 

 present a differentiation, consisting, as they do, of an envelope and 

 special yet homogeneous contents ; others, lastly, are still further 

 differentiated even in the contents. The most important of all 

 these forms which can be included in the category of simple ele- 

 mentary parts, are the cells, which are not only the starting point 

 of every vegetable and animal organism, but, also, either as cells 

 or after undergoing divers metamorphoses, make" up the complete 

 animal body and, in the most simple vegetable and animal forma- 

 tions (unicellular plants and animals), even possess individuality. 

 Compared with the cells, all the other simple elementary parts 

 possess quite a subordinate importance, as far as their direct parti- 

 cipation m the formation of the tissues and organs is concerned: 

 on the other hand, they are undoubtedly of great moment in so 

 far as they are almost all met with in the interior of the cells and 

 participate m their vital processes in a manifold, and, in part, very 

 significant manner. l ' y 



Of the simple elementary parts which at first alone constitute 

 the evolving animal or plant, many unite in the course of develop- 

 ment, m such a manner that they lose their independence, and 

 cease to exis as isolated elements. There thus arise compound 

 forms, each of which corresponds genetically to one entire series of 



