The nutrition of the latter takes place at the expense of the fatty substance which remains after the metamorphosis of the chrysalis into a moth. The dissolution of this fatty substance produces toxins which pass into the urine. Thus the obvious cause of the death of the moth is an acid intoxication by toxic urine secreted in the bladder. As the latter does not empty itself, uræmia becomes inevitable. The majority of moths contain no micro-organisms which could suggest death by infection. The only theoretic objection against a natural death might consist in the existence of "invisible microbes." Indeed, the question of invisible microbes revealed in certain infections perturbed Metchnikoff's mind to such an extent that, during his last illness, he used to say that it would have been a curse to his ulterior activity, a sort of ghost preventing all definite conclusions in problems connected with the absence or presence of microbes. The last word on natural death, he said, will only be spoken when, owing to the improvement of the microscope, those microbes which are as yet invisible to us will become visible. Nevertheless, as far as can be judged at present, the death of the _Bombyx mori_ is due, not to external causes, but to the structure of the insect itself, and is therefore a natural death. During these holidays, Metchnikoff also wrote reminiscences of his friend the physiologist Setchénoff.[30] [30] In the Russian Review, _Messenger of Europe_. We went quietly for fairly long walks; Metchnikoff rested on the shores of his favourite lake (Vilpert), and his health was very satisfactory. After the intense heat, some rain came and the weather became ideal; there was a perceptible lull in nature; the underwood was becoming purple with heather; the corn was ripening; harvest had begun, and sheaves stood up in the fields. All was calm and peaceful; we never tired of the charm of the forest, of the fields, of the beautiful rustic surroundings, and our souls sang in unison with Nature.... Suddenly, like a flash of lightning in the pure sky, the news of the war burst out! The possibility had so often been mentioned in late years that no one believed in it. Even now, on the eve of the catastrophe, it was hoped that all would settle down.... Until the last moment Metchnikoff refused to believe in it; he could not admit that a pacific solution was impossible. "How is it possible that in Europe, in a civilised country, mutual interests should not be reconciled without killing?" he said. "A war would be madness, even from the point of view of Germany, who risks having to face three great powers. No, war is not possible." And yet war was spreading all over Europe.