SOURCES OF DEMAND FOR ALIMENT. 477 



character becomes perceptible enough among many animals, in which it ac- 

 quires a powerfully-disagreeable odour under the influence of fear; and thus 

 answers the purpose, which is effected in others by a peculiar secretion. It 

 is a prevalent, and perhaps not an ill-founded opinion, that melancholy and 

 jealousy have a tendency to increase the quantity, and to vitiate the quality, 

 of the biliary fluid ; perhaps the disorder of the organic function is more com- 

 monly the source of the former emotion, than its consequence ; but it is cer- 

 tain that the indulgence of these feelings has a decidedly morbific effect, by 

 disordering the digestive processes, and thus reacts upon the nervous system 

 by impairing its healthy nutrition. On the influence of mental emotion in 

 the Mother, on the Foetus in utero, some remarks will be offered hereafter 

 ( 938). 



CHAPTER X. 



OF FOOD, AND THE DIGESTIVE PROCESS. 



1. Sources of the Demand for JHiment. Hunger and Thirst. 



629. THE dependence of all Organized beings upon a supply of aliment, 

 in the first place for the development of their fabric, and in the second for the 

 maintenance of their activity, is a circumstance of such a familiar character, 

 that it might not seem worth while to dwell upon it. Nevertheless the in- 

 quiry into the purposes which the aliment serves in the economy, and into 

 the relative values of different articles of food, cannot be advantageously pro- 

 secuted, until we have first determined, with more precision, the causes 

 which occasion the demand to be set up. These will be now briefly enume- 

 rated. 



630. In the first place, a due supply of aliment is required, for the fifct 

 development of the germ into the adult fabric. In all instances, the essen- 

 tial character of the act of Reproduction appears to be the liberation or setting- 

 free of a cell-germ ; which, according to the character of the being that gave 

 origin to it, may be destined to evolve, either a simple cell (as in the lowest 

 Cryptogamic Plants), a congeries of cells having a certain degree of variety 

 of form and of difference of function (as in the higher classes of the Vegetable 

 kingdom), or a complex fabric, composed of an immense variety of parts, 

 most of them departing widely, in appearance at least, from the original cellu- 

 lar type, and destined to perform a vast variety of actions, as we see in the 

 perfectly developed organism of the higher Animals. The materials which 

 are subservient to this evolution, are all derived from the external world ; 

 either immediately, or through the medium of the parent. The germs of the 

 lowly Cryptogamia are thrown at once upon the world (so to speak), to obtain 

 their own livelihood ; and they themselves occasion the combination of the 

 inorganic elements, which they there meet with, into the organic compounds, 

 which are to be applied to the development of their simple organisms. In 

 the Flowering Plants, on the other hand, the germ is at first supplied with a 

 store of nutriment, which has already undergone this preparation, by the 

 agency of the parent ; and this store, laid up in the seed, is employed in the 

 development of the fabric of the young plant, until its organs are sufficiently 

 evolved to enable it to perform the same processes for itself. The same plan 



