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 
everywhere, 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, ete., 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 naturally 
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. 
