OP VITAL ACTIONS IN GENERAL. 31 



body. And when we come to consider the proper Animal functions, we 

 shall find that they are not so far removed in their essential nature from 

 those of Plants, but that they may be ranked under the same category, 

 and regarded as different manifestations of the same original forces. 

 A Cell, then, in Physiological language, is a closed 

 vesicle or minute bag, formed by a membrane in 

 which no definite structure can be discerned, and 

 having a cavity which may contain matters of varia- 

 ble consistence. Such a cell constitutes the whole 

 organism of such simple plants as the Protococcus 

 nivalis (' red snow'), or Palmella cruenta (' gory 

 dew') ; for although the patches of this kind of vege- 

 tation, which attract our notice, are made up of vast 

 aggregations of such cells, yet they have no depen- 

 dence upon one another, and the actions of each are 

 an exact repetition of those of the rest. In such 

 a cell, every organized fabric, however corn- 

 complex, originates. The vast tree, almost a forest in itself, and the 

 feeling, thinking, intelligent man, spring from a germ, that differs in no 

 obvious particular from the permanent condition of one of these lowly 

 beings. But whilst the powers of the latter are restricted, as we shall 

 see, to the continual multiplication of new and distinct individuals like 

 itself, those of the former enable it to produce new cells that remain in' 

 closer connexion with each other ; and these are gradually converted, 

 by various transformations of their own, into the diversified elements of 

 a complex fabric. The most highly-organized being, however, will be 

 shown to consist in great part of cells that have undergone no such trans- 

 formation, amongst which the different functions performed by the indi- 

 vidual in the case just cited, are distributed, so to speak ; so that each 

 cell has its particular object in the general economy, whilst the history 

 of its own life is essentially the same as if it were maintaining a separate 

 existence. 



27. We shall now examine, then, the history of the solitary cell of 

 one of the simplest Cryptogamic Plants, from its first development to 

 its final decay ; in other words, we shall note those Vital Phenomena, 

 which are as distinct from those of any inorganic body, as is its organ- 

 ized structure (simple as it appears) from the mere aggregation of par- 

 ticles in a mineral mass. In the first place, the cell takes its origin 

 from a germ, which may be a minute molecule, that cannot be seen 

 without a microscope of high power.* This molecule appears, in its 

 earliest condition, to be a simple homogeneous particle, of spherical 

 form ; but it gradually increases in size ; and a distinction becomes 

 apparent between its transparent exterior and its coloured interior. 

 Thus we have the first indication of the cell-wall, and the cavity. As 

 the enlargement proceeds, the distinction becomes more obvious ; the 

 cell-wall is seen to be of extreme tenuity and perfectly transparent, and 

 to be homogeneous in its texture ; whilst the contents of the cavity are 



* The modes in which new cells may be generated are various ; but the above exam- 

 ple is purposely drawn from one of those simple Algge, whose usual mode of multipli- 

 cation is by " zoospores." (See the Author's " Principles of Physiology," %\ 139-144.) 



