NUTRITION EXPLAINS ADAPTATION. 223 



quantity of food. Our mental activity, the activity of our 

 understanding and of our imagination, is quite different 

 accordingly as we have taken tea or coffee, wine or beer, 

 before or during our work. Our moods, wishes, and feelings 

 are quite different when we are hungry and when we are 

 satisfied. The national character of Englishmen and 

 Gauchos, in South America, who live principally on meat 

 and food rich in nitrogen, is wholly different from that of 

 the Irish, feeding on potatoes, and that of the Chinese, living 

 on rice, both of whom take food deficient in nitrogen. The 

 latter also form much more fat than the former. Here, as 

 everjnvhere, the variations of the mind go hand in hand 

 with the corresponding transformations of the body ; both 

 are produced by purely material causes. But all other 

 organisms, in the same way as man, are varied and changed 

 by the different influences of nutrition. It is well known 

 that we can change in an arbitrary way the form, size, 

 colour, etc., of our cultivated plants and domestic animals, 

 by change of food; that, for example, we can take from, 

 or give to a plant definite qualities, accordingly as we 

 expose it to a greater or less degree of sunlight and moisture. 

 As these phenomena are generally widely known, and as we 

 shall proceed presently to the consideration of the different 

 laws of adaptation, we will not dwell here any longer on 

 the general facts of variation. 



As the different laws of transmission may be naturaUy 

 divided into the two series of conservative and progressive 

 transmission, so we may also distinguish between two series 

 of the laws of adaptation, first, the series of laws of indirect, 

 and secondly, the series of laws of direct adaptation. The 

 latter may also be called the laws of actual, and the former 

 the laws of potential, adaptation. 



