out how the organism defends itself when disharmonious substances introduce a disturbing element into its metabolism, so delicately poised and harmonized even in its finest details. In these problems the most varied hypotheses regarding cellular metabolism are to be met with. The more the biologist enlarges the limits of his researches, and the more he follows up all general phenomena, the more may he venture to hope that he will gain new means and new lines for the study of special processes. The appearance of the defensive ferments in the animal organism, when it is invaded by substances that are out of harmony either with its body, with its blood, or even with some of its cells, gives us an insight into many problems of pathology, and particularly into those of immunity. Every approximation of fields of thought that are at first sight dissimilar, arising out of observations which allow us to presume common reactions and common processes, must be met with approval. It will then be possible that, by an exchange of results based on very different methods and hypotheses, we shall acquire a wide outlook over the fundamental properties of cells of different origin.
Prolonged observations on a particular case of definite disease will be of the greatest importance. It would be absurd to investigate, say, a hundred
