that it is at a quite definite stage that the by-products of metabolism are passed by the cells into the lymph channels, and so into the blood system. The individual cell is in this sense responsible for the constant composition of the contents of the blood, in the same way as the cells of the bowels with their respective ferments.
Here, again, the animal organism controls important weapons of defence which may correct any possible errors. Between the blood and the cells of the body lies the lymph. The latter is the first to receive the substances supplied by the individual cells, and controls them by means of its accessory apparatus, namely, the lymph cells and the glands. Some of the substances are further disintegrated or transformed in some other way, and, perhaps, even utilized for various syntheses. From this point of view we may look upon the lymph as a powerful means of defence, whose aid is particularly valuable in preventing the infusion into the blood of compounds that are both quantitatively and qualitatively unsuitable. From all sides care is taken that only normally suitable substances shall appear in the blood.
From this point of view we may distinguish substances that are "out of harmony with the body," i.e., such compounds as, in their structure and configuration, show no correspondence with the con-
