38 BIOLOGY. [Boox i. 



more profoundly the mechanism of the vital acts ; it has taught 

 it to refer them to their ultimate agents, that is, to the histo- 

 logical elements themselves, which vary in function and in form 

 in complex beings, and which we must consider as playing a part 

 in the mechanism of organised beings, analogous to that of atoms 

 in chemical aggregates. As Schwann has said, " Forasmuch 

 as the primary elementary forms of all organisms are cells,, 

 the fundamental force of all organisms reduces itself to the 

 fundamental force of cells." (Mikroskopische Untersuchungen, 

 1838.) 



The cell, properly so called, of which we have given above a 

 succinct description, is a sort of schematic type, scarcely existing 

 in anything except rudimentary beings and tissues. If we study 

 the cell either as a complex organism, or in the hierarchical 

 series of organisms, we see it in effect modifying itself, putting 

 on different forms when assuming diversified functions. Finally, 

 another type of histological element appears : it is the fibre, a 

 microscopical element likewise, springing evidently from the cell 

 in certain cases, where the cells have merely been elongated by 

 juxtaposing and cementing themselves end to end. These deri- 

 vative fibres exist manifestly in plants, in which they often 

 hollow a passage for themselves as canals. According to Ch. 

 Robin, there is a different process in animals. Here the fibres, 

 with all their essential attributes, would seem to be present at 

 the very dawn of the embryonic life, forming themselves spon- 

 taneously by genesis, at the expense of the blastematic liquids 

 secreted by cells. As there are various species of cells, there 

 are also various species of fibres ; but the true typical fibres, well 

 specialised, are found scarcely anywhere except in the animal king- 

 dom. We purpose speaking further on at greater length of cer- 

 tain species of fibres, muscular fibres, nervous fibres, and so on. 



In sum, passing by some amorphous organised types, points of 

 union of a sort between the living world and the non-organised 

 world, we must consider every complex organism as being con- 

 stituted by a great number of individuals, living, microscopic. 



