especially the testes, approach maturity, replaced by protamines, which consist nearly exclusively of di-amino-acids. We see, in this example, how cells of a characteristic structure transfer their material to the blood circulation in a profoundly modified form. First of all substances are produced that are in harmony with the plasma, and these are transferred to the cells of the sexual glands by means of the circulation. These glands take up the indifferent substances, and from them build up products specific to themselves. There is no doubt that similar processes play a part in normal metabolism. Sometimes one group of cells will help another in this way, particularly in cases where the supply of nourishment is delayed for some time.
The reconstruction of substances of every kind from products that are harmonious to the plasma and the lymph is demonstrated by every growing hair and every growing nail. Every new blood corpuscle tells us of far-reaching transformations; and every secretion—whether produced directly, as in the case of saliva or milk, or manifested when a fistula is produced by surgical means, or whether it forms a so-called internal secretion, choosing the blood or the lymph for its path of action—every one of these gives evidence of powerful disintegrations, integrations, or transformations. When thousands and thousands of leucocytes hurry forth against an invasion of
