few of them. In the first place it would be desirable to find out where the defensive ferments arise, and whether they can be met with inside the individual cells themselves. It is, for instance, conceivable that the walls of the intestine, and perhaps also the cells of the liver, are always provided with definite ferments for the purpose of further reducing substances which, though insufficiently decomposed, pass through the gut epithelium; and it is very probable that the leucocytes play an important part in this connection. They circulate rapidly through the whole organism. They are to be looked on as protective organs, which, to use a metaphor, overlook everything with a view to finding out whether order prevails. Some products are eliminated by being absorbed into the body of the leucocytes (phagocytosis); others are attacked by their ferments, and so broken up, and deprived of their characteristic structure. Finally, as mentioned before, the separate organs have to be considered, particularly the kidneys.
But the most important advantage of the methods we have described is, that they will enable us to study the reciprocal dependence of individual organs. Suppose, for instance, we remove the thyroid gland; we then anticipate that another organ, some of whose functions depend on this gland, will have its metabolism interfered with, and will in consequence give
