have cells before us which are neither subordinate to, nor co-ordinate with, the rest of the complex of cells. These cells have obviously reached a definite state of independence, nor do they maintain any direct relations with the different cells of the body. They are, so to say, outside the association of the cells of a particular organ, nor is there any doubt that they produce secretions, the products of their metabolism, which are out of harmony with the blood plasma. And we can well believe that here, too, cells decay, and products pass into the blood which are quite out of harmony with the plasma.
These ideas afford the possibility of studying, within the body, the action of disharmonious organisms of every description, especially of micro-organisms, and their relations towards the rest of the body cells, from a purely physiological point of view. It seems to us well worth while to follow up these conceptions, and to attempt, by means of direct experiments and observations, to bind together in closer relations the two fields of research that are covered by physiology and the study of immunity.
In the first place, we set ourselves the question: To what measures does an animal organism resort if substances penetrate into its body, and particularly into its blood, which are out of harmony with the species as a whole, or else only with the blood or
