INFLUENCE OF VARIATIONS IN SUPPLY- OF FOOD. 241 



415. The demand for food is increased by any cause, which creates 

 an unusual drain or waste in the system. Thus an extensive suppu- 

 rating action can be sustained only by a large supply of highly-nutri- 

 tious food. The mother, who has to furnish the daily supply of milk 

 which constitutes the sole support of her offspring, needs an unusual 

 sustenance for this purpose. And there are states of the system, in 

 which the solid tissues seem to possess an unusual tendency to decom- 

 position, and in which an increased supply of aliment is therefore re- 

 quired. This is the case, for example, in diabetes ; one of the first 

 symptoms of which disease is the craving appetite, that seems as if it 

 would never be satisfied. And there can be no doubt that, putting 

 aside all the other circumstances that have been alluded to, there is 

 much difference amongst individuals, in regard to the rapidity of the 

 changes which their organism undergoes, and the amount of food re- 

 quired for its maintenance. 



416. The influence of the supply of food upon the size of the indivi- 

 dual, is very evident in the Vegetable kingdom-; and it is most strikingly 

 manifested, when a plant naturally growing in a poor dry soil is trans- 

 ferred to a damp rich one, or when we contrast two or more individuals 

 of the same species, growing in localities of opposite characters. Thus, 

 says Mr. Ward, " I have gathered, on the chalky borders of a wood in 

 Kent, perfect specimens in full flower of Erythrcea Centaurium (Com- 

 mon Centaury), not more than half an inch in height ; consisting of one 

 or two pairs of most minute leaves, with one solitary flower : these were 

 growing on the bare chalk. By tracing the plant towards and in the 

 wood, I found it gradually increasing in size, until its full development 

 was attained in the open parts of the wood, where it became a glorious 

 plant, four or five feet in elevation, and covered with hundreds of flow- 

 ers." On the other hand, by starvation, naturally or artificially induced, 

 Plants may be dwarfed, or reduced in stature : thus the Dahlia has been 

 diminished from six feet to two ; the Spruce Fur from a lofty tree to a 

 pigmy bush ; and many of the trees of plains become more and more 

 dwarfish as they ascend mountains, till at length they exist as mere 

 underwood. Part of this effect, however, is doubtless to be attributed 

 to diminished temperature ; which, as already remarked, concurs with 

 deficiency of food in producing inferiority of size. 



417. Variations in the supply of food would not appear to be effec- 

 tual in producing a corresponding variety of size in the Animal king- 

 dom : this is not, however, because animals are ; in any degree less 

 dependent than Plants upon a due supply of food ; but because such a 

 limitation of the supply, as would dwarf a Plant to any considerable 

 extent, would be fatal to the life of an Animal. On the other hand, 

 an excess of food, which (under favourable circumstances), would pro- 

 duce great increase in the size of the Plant, would have no correspond- 

 ing influence on the Animal ; for its size appears to be restrained within 

 much narrower limits, its period of growth being restricted to the early 

 part of its life, and the dimensions proper to the species being rarely 

 exceeded in any great degree. Even in -the case of giant individuals, 

 it does not appear that the excess of size is produced by an over-supply 

 of food ; but that the larger supply of food taken in is called for by the 



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