backwards the line of causation, and thus to display, if possible, its manner of origin. This is the more necessary with the lower animals, where so much is innate.'[2] [2] Maudsley on the Physiology and Pathology of the Mind, p. 73. The special laws of inheritance are indeed as yet unknown. All which is clear, and all which is to my purpose is, that there is a tendency, a probability, greater or less according to circumstances, but always considerable, that the descendants of cultivated parents will have, by born nervous organisation, a greater aptitude for cultivation than the descendants of such as are not cultivated; and that this tendency augments, in some enhanced ratio, for many generations. I do not think any who do not acquire--and it takes a hard effort to acquire--this notion of a transmitted nerve element will ever understand 'the connective tissue' of civilisation. We have here the continuous force which binds age to age, which enables each to begin with some improvement on the last, if the last did itself improve; which makes each civilisation not a set of detached dots, but a line of colour, surely enhancing shade by shade. There is, by this doctrine, a physical cause of improvement from generation to generation: and no imagination which has apprehended it can forget it; but unless you appreciate that cause in its subtle materialism, unless you see it, as it were, playing upon the nerves of men, and, age after age, making nicer music from finer chords, you cannot comprehend the principle of inheritance either in its mystery or its power. These principles are quite independent of any theory as to the nature of matter, or the nature of mind. They are as true upon the theory that mind acts on matter--though separate and altogether different from it--as upon the theory of Bishop Berkeley that there is no matter, but only mind; or upon the contrary theory--that there is no mind, but only matter; or upon the yet subtler theory now often held--that both mind and matter are different modifications of some one tertium quid, some hidden thing or force. All these theories admit--indeed they are but various theories to account for--the fact that what we call matter has consequences in what we call mind, and that what we call mind produces results in what we call matter; and the doctrines I quote assume only that. Our mind in some strange way acts on our nerves, and our nerves in some equally strange way store up the consequences, and somehow the result, as a rule and commonly enough, goes down to our descendants; these primitive facts all theories admit, and all of them labour to explain.