O'SHEA — ASPECTS OP MENTAL ECONOMY. 139 



CHAPTER VI. 



INDIVIDUAL PECULIARITIES IN DIGESTIVE CAPACITIES. 



§1. The Theory of Individual Differences. — There seem to 

 be two great forces that vie with one another in planning and 

 directing the construction of every new being ushered into the 

 world. The first is heredity, Which seeks to reproduce without 

 modification in the offspring the characteristics of the parents ; 

 the second is variation, which seeks to differentiate the young 

 from their ancestors — to beget in them modified structures and 

 functions. 1 As a result of the interaction of these forces it 

 happens that while members of the human species, for instance, 

 are much alike, still each is probably distinguished by some 

 purely individual features either in the architecture of the body, 

 in the workings of the vital machinery, or in mental tendency 

 and capacity. 2 These differences are probably as marked in 

 respect of digestive functions as of any other; and it is not dif- 

 ficult to appreciate this when it is realized that the transforma- 

 tion of food is brought about through the offices of various di- 

 gestive fluids. Each food element has its particular digestive 

 agent, — starch requiring a special one, albumen another, fat 

 .another. Now, it happens that people differ regarding the 

 quantity and quality of each of these digestive agents ; this per- 

 son falls short on the one essential for the disposition of starch, 

 another generates free hydrochloric acid in excess of that which 

 is actuallv needed or which is conducive to the well-being of the 

 organism, and so on. It results then that we all have our ldio- 



*Cf. Bateson, Materials for the Study of Variation, London, 1894, pp. 1-80. 

 Darwin, Origin of Species, entire book ; Hoffding, Outlines of Psychology, p. 348, 



■et seq. 



2 See for a discussion of individuality in the mental sphere, — Bain : A Study 

 of Character, London, 1863 ; Ribot : Psychology of the Emotions, chap. XII ; 

 Paulhan : Les Characteres ; Perez: Caractere de I'enfant et de I'homme; Lotze : 

 Microcosmus, Bk. VI, chap. II; Queyrat : L' imagination chez I'enfant; Galton ; 

 Mental Faculty, chap, on Mental Imagery. 



