Another point must be attended to, in order to secure that the brain be nourished by healthy blood. The blood receives and gets rid of the waste of the issues, and one of the most important agents by means of which it does this necessary scavenger’s work is the skin. Millions of invisible pores perforate the skin, each the mouth of a minute many-folded tube, and each such pore is employed without a moment’s cessation, while the body is in health, in discharging perspiration — that is, the waste of the tissues — upon the skin.