36 NATURE AND OBJECTS OF PHYSIOLOGICAL SCIENCE. 



of a living cell, as is the growth of its wall ; and it must never be left 

 out of view, when considering the history of its development. 



36. Every kind of cell has its own specific endowments ; and gene- 

 rates in its interior a compound peculiar to itself. The nature of this 

 compound is much less dependent upon the nutrient materials which 

 are supplied to the cell, than upon the original inherent powers of the 

 cell itself, derived from its germ. Thus we find that the "red snow" 

 and " gory dew" invariably form a peculiar red secretion ; and that they 

 will only grow where they can obtain, from the air and moisture around, 

 the elements of that secretion. Again, the "yeast-plant" invariably 

 forms a secretion analogous to animal proteine ; and it will only grow 

 in a fluid which supplies it with the materials of that substance. Hence 

 the "red snow" would not grow in a fermentible saccharine fluid; nor 

 would the "yeast plant" vegetate on damp cold surfaces. Yet there is 

 little difference, if any, between their cell-walls, in regard to chemical 

 composition. So, also, we shall find hereafter, that one set of cells in 

 the Animal body will draw into themselves, during the process of growth, 

 the elements of bile ; another, the elements of milk ; another, fatty 

 matter ; and so on : the peculiar endowments of each being derived from 

 their several germs, which seem to have an attraction for these sub- 

 stances respectively, and which thus draw them together ; whilst the 

 cell-wall appears to have a uniform composition in all instances. 



37. The term Secretion, or setting apart, is commonly applied to this 

 operation, to distinguish it from Nutrition or growth ; but it is obvious 

 from what has now been stated, that the act of secretion is in reality 

 the increase or growth of the cell-contents, just as the process of en- 

 largement is the increase or growth of the cell-wall ; and that the two 

 together make up the whole proces'fe of Nutrition, which cannot be pro- 

 perly understood, unless both are taken into account. It is to be remem- 

 bered, however, that the contents of the cell may not be destined to 

 undergo organization ; indeed we shall find hereafter, that the main use 

 of certain cells is to draw off from the circulating fluid such materials 

 as are incapable of organization ; and the operation may be so far attri- 

 buted, therefore, to the agency of Chemical forces. But we shall find 

 that, in other instances, the cell-contents are destined to undergo orga- 

 nization, and this either within the parent cell, or after they leave it ; 

 here, then, we must recognise a distinct vitalizing agency, as exerted 

 by the cell upon its contents. 



38. This organizing or vitalizing influence must be exerted upon a 

 certain portion of the contents of every cell that is capable of repro- 

 ducing itself; for it is in this manner that those germs are produced, in 

 which all the wonderful properties are inherent, that are destined to 

 manifest themselves, when they are set free from the parent-cell. This 

 power of Reproduction is one of those, which most remarkably distin- 

 guishes the living being ; and we shall find that, in the highest Animal, 

 as in the humblest Plant, it essentially consists in the preparation of a 

 cell-germ, which, when set free, gradually developes itself into a struc- 

 ture like that from which it sprang. The reproductive molecules or 

 cell-germs are formed, like the tissue and the contents of the parent-cell, 

 from the nutrient materials which it has the power of bringing together 



