[19] Do you not see that our bodies do not use solid and costly food before they have first, in their age of infancy, used such as had no variety, and consisted merely of milk? And, in the same way, think also that infantine food is prepared for the soul, namely the encyclical sciences, and the contemplations which are directed to each of them; but that the more perfect and becoming food, namely the virtues, is prepared for those who are really full-grown men.