This is how Metchnikoff had reconciled the apparent disagreement of Pfeiffer's phenomenon with the phagocyte doctrine: he demonstrated, by a series of experiments, that the extracellular destruction of the cholera vibriones in the peritoneum of a guinea-pig vaccinated against cholera, did in no wise depend on the _chemical_ properties of the blood serum, but was simply due to the digestive juices which had escaped from the inside of the leucocytes, damaged by the intraperitoneal injection. Those digestive juices, or _cytases_, poured into the peritoneal liquid were what killed the injected cholera vibriones and transformed them into "Pfeiffer's granulations." On the other hand, if by means of various precautions the phagocytes were left unmolested, the extracellular destruction did not take place and the vibriones were digested within the phagocytes. Metchnikoff used other experiments to prove that the bactericidal property of blood juices did not exist without intervention from the phagocytes. For instance, in a guinea-pig vaccinated against cholera, the bacilli are not destroyed if they are injected into parts of the organism that are devoid of pre-existing phagocytes, such as in the subcutaneous tissue, in the anterior chamber of the eye or in an aseptically-obtained oedema. On the other hand, if, in the same medium, some exudate is injected containing damaged leucocytes from which the digestive juice is leaking, the vibriones introduced are destroyed. The same results are obtained _in vitro_. All these experiments proved that the extracellular destruction of the cholera vibrio was accomplished by the digestive juices which had passed from the phagocytes into the humors and not at all through a special property of those humors. Once again the phagocyte theory rose triumphant from the test. After having finally proved that it is by means of its phagocytes that the organism fights _microbes_, Metchnikoff wished to find out whether it was by the same process that it struggled with their poisons, or _toxins_. This problem, far more difficult to solve, took him many years' study. Whilst every phase of the phagocytes' struggle against microbes can be followed with the eyes, it is impossible to do so where poisons are concerned, since they are invisible; it is necessary to proceed by a different road.