Immunity against diseases is but one of the manifestations of an immunity on a much larger scale, always based, in final analysis, on the sensitiveness of the living cellular protoplasm. The sensitiveness of the nervous cells extends this phenomenon to the psychical domain. They also are capable of becoming accustomed to external irritations of all kinds, hence constituting a psychical immunity for the organism. We all know that one can become accustomed to many painful or violent sensations; and, as Metchnikoff says: "... It is very probable that the whole gamut of Habit, starting from the unicellular beings, who accustom themselves to live in an unsuitable medium, to cultured men who acquire the habit of not believing in human justice, rests on one and the same fundamental property of living matter." CHAPTER XXVII Private sorrows--Death of Pasteur, 1895--Ill-health--Senile atrophies--Premature death--Orthobiosis--Syphilis--Acquisition of anthropoid apes. Metchnikoff's health had suffered from the numerous emotions provoked by the struggle in defence of the phagocyte doctrine and also from a series of sad events. In 1893, sickness and death fell upon our family; I lost a sister and a brother at a short interval and had myself to undergo a serious operation. My husband nursed me night and day, as a mother might have done, and went through the deepest anxiety on account of post-operative complications. All this told on him all the more that he had just endured cruel moral suffering during the experiments on cholera mentioned above. In 1894, an agricultural crisis in Russia influenced our material situation and gave him many worries. In the autumn of 1895, M. Pasteur's health became worse and, soon afterwards, he died. This series of calamities depressed Metchnikoff, his old cardiac trouble returned, and he again became a prey to insomnia. We spent part of the holidays in the mountains, thinking it might do him good, but he did not care for a prolonged rest; he was preoccupied by the thought of his interrupted experiments and only thought of returning to the laboratory. In 1898, he had some disquieting symptoms of kidney trouble, a little albumen. He consulted the celebrated German physician, von Noorden, who found nothing serious, but this did not reassure him and he continued to worry about himself.