Far more important in view of our immediate object is the _influence exerted by Climate on the individual activity of the genital organs_, and here again we have in the first place to fix our eyes on Asia and Egypt. The burning rays of the sun to which these regions and their inhabitants are exposed, increase in a marked way the activity of the skin, and of course in the same proportion do the secretions from the mucous surfaces become less in quantity, but their product more highly charged in quality. Then, this being the case, a certain acridity or corroding quality of the secretion is readily set up, often making itself noticeable by a characteristic smell. This same influence must equally manifest itself in the mucous membrane of the inner parts of the genitals, and vaginal mucus accordingly acquire an acrid quality[147], if it is not removed pretty frequently from the surface of the membrane, and becoming as it were rancid, exert a corrosive effect on everything it comes in contact with[148]. Now shortly before as well as shortly after the commencement of menstruation the secretion of mucus in the genitals is increased, and thus the menstrual blood, having in any case a tendency to decomposition, will mingle with this acrid, strong-smelling mucous discharge, and in this way assume a foul, acrid character itself[149]. This is the origin of the ill repute into which menstrual blood, and this especially in hot climates, has fallen from the earliest times onwards, for no doubt the virulent qualities alleged against it really belong to it solely and entirely as a result of the admixture with it of this vaginal mucus. Sea-water and fresh river-water are each of them separately innocuous for health, but mix them together so as to make brackish water, and the exhalations given off become highly detrimental!