318 cosmic rniLosornY. lpt. u. 



a change from a state of diffusion to a state of aggregation ; 

 and the converse change, from aggregation to diffusion, must 

 "be the change by virtue of which the object again becomes 

 imperceptible. If, for example, we study a cloud, we find 

 that a complete history of it is contained in the explanation 

 of its concentration from millions of particles of aqueous 

 vapour, and its subsequent dissipation into a host of such par- 

 ticles. In like manner, if we study an organism, we find that 

 from germination to final decomposition, its career consists of 

 an epoch of concentration followed by an epoch of diffusion, 

 A very small portion of its constituent matter pre-existed in 

 a concentrated form in the embryo ; by far the greater 

 portion pre-existed in the shape of dispersed nitrogenous 

 and carbonaceous compounds, which the growing organism 

 has incorporated with its own structure. Nay, even if we 

 inquire into the previous history of the small portion which 

 was concentrated in the embryo, we may trace it back to 

 an epoch at which it existed in a state of dispersion, as 

 food not yet assimilated by the parent organism. If the 

 organism in question belong to an order of carnivorous 

 animals, we shall indeed have to follow its constituent ele- 

 ments through a series of phases of concentration ; through' 

 the tissues of sundry herbivorous animals upon which it has 

 fed, and again through the tissues of numerous plants upon 

 which these have in turn subsisted ; but in the end we shall 

 always arrive at the host of dispersed molecules which these 

 organisms have eliminated from the breezes and the trickling 

 streamlets by which their leaves and roots were formerly 

 bathed. On the other hand, when the animal dies, and the 

 tree falls to decay, the particles of which they consist are 

 again dispersed ; and though they may again be brought 

 together in new combinations, the career of the organism 

 in question is ended with this dispersal. Again if, instead 

 of a transient cloud or a mobile organism, we contemplate 

 an apparently permanent and immobile rock, we are led to a 



