Memory means a change impressed more or less deeply on the grey surface of the brain.

A change. Those "images" which Darwin tells us are continually passing through the mind have actually made a change in the brain. That is to say, they have made a change in the mind: they have made a change in the personality.

After showing how a singer learns to produce a note properly by practice until he is almost incapable of producing it improperly, and until its proper production has become mechanical, Dr. Saleeby says:

The effect of practice, as in any other art, mechanical, mental, or both, has been so to alter the constitution of the nerve cells as to produce a new mode of action.

The nerve cells have been re-arranged, and the habit of the person has been altered. He is no longer quite the same person. He now acts and thinks differently.

Now, these changes in the arrangement of the brain cells and fibres may be looked upon as the building up of the moral wall. And the desires and aversions are like the rising and falling tide.

And the tide of our desires is a tide of nature. Because our desires and aversions seem to work by reflex action. What is reflex action?

Reflex action, as I use the term here, is the mechanical action of the nerves. We do not grow hungry, or thirsty, or angry, or compassionate on purpose: we do not fall in love on purpose. The stomach, working, like the heart and lungs, by reflex action, without our knowledge or direction, uses up the food, and our nerves demand more. The desire for food, for love, for revenge, is due to reflex action. The desire makes itself felt first without our asking, and we have to refuse or to grant its request after it is made.

We do not say: "Behold, there is a pretty face: I will be attracted by it." We cannot help being attracted by the face that attracts us, any more than we can help being hungry. The face attracts us, more or less, and we decide to seek out its owner, according to the strength of the attraction and of the reason for resisting the attraction. We see a diamond. We do not say: "There is a diamond. I will not think it beautiful." We cannot think it anything but beautiful; but whether or not we shall buy it or steal it depends upon the strength of our desire and the strength of the reasons against gratifying that desire.

Now, let us see how these conflicting ideas act. A man sees a beautiful woman, and desires to see more of her. But he fears if he sees much of her he will fall in love with her. And he is engaged to marry another woman. What goes on in his mind? Memory reminds him that he is engaged, and that it would be "wrong" to follow his desire. And every time the temptation draws him to follow his desire he calls up the "image" of the other woman, and he calls up the images of old lessons, of old thoughts, of old opinions read and heard by him. And the stronger the temptation grows the more earnestly does he invoke these images. Now, what does all this show? It shows the contest between the reflex action of desire, backed by the memories of love's pleasures, on the one part; and, on the other part, of the moral feelings of memories of what he has learnt or thought to be right and wrong. It is then a battle between memory and desire.