Besides the better known products of metabolism the properties of which are fairly well understood, there is a class of bodies the functions of which are not so well known, the study of which is now engrossing the ablest biologists of the present time.

The healthy organism has the power of producing substances which are antagonistic to foreign cellular products and derivatives. These are for the most part of an albuminous nature and have the power of neutralizing poisons and ferments, of injuring or destroying cells, of causing the cessation of cellular motion, and of agglutination, precipitation and coagulation. These are called respectively anti-toxins or anti-enzymes, cyto-toxins or cyto-lysins, agglutinins, precipitins and coagulins. Of these the cyto-lysins are particularly concerned in auto-intoxication. The lysins are specific not only for the species but also for the cellular group from which they proceed, and they take their name from their origin. The toxin derived from the renal cells are termed nephro-toxins, those from the thyroid thyreo-toxins, and those from the placenta syncytio-toxins. A lysin contains two bodies: one. called the complement, actually injures or destroys foreign cells, but it is incapable of action without the assistance of the other component called the intermediary body or amboceptor. These two elements exist independently and one may be artificially removed without affecting the other. Now the intermediary body may be considered as having a single cyto-philic affinity and a number of complementophilic affinities, the former being specialized for association with bacterial or other cells, the latter for combination with the various complements of other anti-bodies. The side or lateral chains are the receptors or amboceptors and the ability of an organism to produce an autotoxin depends upon the formation of a substance that will set free a side chain. The absence of suitable receptors explains immunity to corresponding poisons. If then in the life history of a cell there is brought to it in the blood stream any substance capable of doing this, the intermediary body thus formed acts in conjunction with the complement and cytolysis takes place. The perfect organism may be considered as being in a continued condition of immunity from self-generated poisons, damage being done to the tissues only when immune bodies are not forthcoming to meet the invading poison, whether this be from within or from without.

This is in brief the principle upon which the cytolysins act and their operations are studied by experiments upon one animal with the elaborated serum of another. Now it seems reasonable to suppose that the emanations from a tissue may under certain conditions act upon the cells of another part, complementary bodies striving through their affinities to associate themselves with the receptors or specialized portions of the cells through the intervention of the intermediary bodies, without which such a union cannot take place.

The researches of Lindemann (1) show that iso-lysins are a reality and throw much light upon the probable origin of certain phases of disease. In his experiments the kidney of a rabbit was emulsified and introduced into the peritoneal cavity of a guinea pig. The serum of this animal when injected into rabbits caused albuminuria, anuria and death, and the histological examination showed disintegration and necrosis of the convoluted tubules of the kidneys, a state common in experiments with the better known renal poisons. He also found that the serum of dogs in which nephritis had been artificially induced by the injection of potassium chromate, caused nephritis terminating in death when injected into other dogs. It has furthermore been found that the ligation of one of the ureters of a rabbit is followed by a change in the nephritis-producing power of its blood serum. Twenty-four days after ligation the serum caused distinct albuminuria which persisted for four days, and forty-one days after ligation the injection into a perfectly healthy rabbit, free from any evidence of nephritis, was followed by a large amount of albumen in the urine, and the examination of the kidneys showed necrosis, vacuolization of the convoluted tubules, disintegration of the epithelial nuclei, and, in the straight tubules epithelial casts, the cells of which were so disintegrated as to be almost structureless.

Of absolutely definite auto-lysins we know but little save that the trend of experiment and research points strongly towards them. We look for a more complete realization of these biologic truths, and as the Periodic Law of Mendeljeff predicted undiscovered chemical elements, so does the trend of research indicate that we shall soon know more of these mysterious bodies, the knowledge of which has already been of such inestimable value.