In the case of a little girl eighteen months old, afflicted with infantile spinal paralysis of the left leg, with considerable chill, I made four punctures on the outer side of each arm with a lancet carefully charged with vaccine matter; the inoculation was successful only on the diseased side. Some more recent experiments bear in the same direction. On the other hand, certain medicines quieting to the nervous system, like opium, morphine, chloral, and bromide of potassium, seem also to favor infection.
The influence of the emotions on infection is further susceptible of a direct experimental demonstration. Having under my care a number of weak-minded persons susceptible of taking interest in a monotonous exercise, I profited by the opportunity to try upon a considerable number of animals—pigeons, rabbits, and white mice—the effect of fear, which was excited by means of noise or threatening motions, through several consecutive hours. The experiments may be divided into three groups: 1. The blood of frightened animals and of witnessing animals was sown. While the blood of the latter animals was sterile, that of the former gave in half the cases more or less numerous colonies of microbes. 2. Animals, some of which had been left at rest, and others had been disturbed, were inoculated with cultivations of pathogenic microbes—of carbuncle, hen cholera, pneumo-enteritis of swine, and Fraenkel's pneumococcus. In all the experiments, without exception, the frightened animals died first, if the cultivations were virulent; while if the cultivations were attenuated they alone died or were ill. We have seen animals little susceptible to an infection succumb to it under the influence of fear; frightened pigeons yielded to pneumo-enteritis of swine, while mere witnesses did not appear to be affected at all. 3. On introducing under the skin of the ear or of the brow of rabbits, or under the skin of the wing of pigeons, capillary tubes closed at the end and filled with cultivations of pathogenic microbes or of saprophytes, we discovered considerable differences in the chimiotactic properties of the white globules, according to the condition of the animals. With frightened animals the tubes were often found at the end of thirty-four hours entirely filled with transparent liquid, while with witness animals the tubes containing whitish trails through their whole length were choked at the ends with a compact wad of leucocytes two or three millimetres long. Most of the microbes had disappeared in the case of healthy animals, while a very large number of them remained in the fluid of the other animals, in which the microscope could discover only a very few leucocytes. We are therefore able to show experimentally in frightened animals that one of the conditions of resistance to infection is absent. The study of these facts deserves to be pursued in detail.
We know the influence local traumatisms have on the location