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in the blood were living organisms and the cause of the disease, this did not explain the mode of infection; how the organisms contained in the blood passed to another animal, why the disease occurred on certain farms and the adjoining farms, particularly if they lay higher, were free. Koch showed that in the cultures the organisms grew out into long interlacing threads, and that in these threads spores which were very difficult to destroy developed at intervals; that the organisms grew easily in bouillon, in milk, in blood, and even in an infusion of hay made by soaking this in water. This explained, what had been an enigma before, how the fields became sources of infection. The infection did not spread from animal to animal by contact, but infection took place from eating grass or hay which contained either the bacilli or their spores. When a dead animal was skinned on the field, the bacilli contained in the blood escaped and became mingled with the various fluids which flowed from the body and in which they grew and developed spores. It was shown by Pasteur that even when a carcass was buried the earthworms brought spores developed in the body to the surface and deposited them in their casts, and in this way also the fields became infected. From such a spot of infected earth the spores could be washed by the rains over greater areas and would find opportunity to develop further and form new spores in puddles of water left on the fields, which became a culture medium by the soaking of the dead grass. The contamination of the fields was also brought about by spreading over them the accumulations of stable manure which contained the discharges of the sick cattle. The tendency of the disease to extend to lower-lying adjacent fields was due to the spores being washed from the upper fields to the lower by the spring freshets. Meanwhile Pasteur had discovered that by growing the organisms at higher temperatures than the animal body, it was possible to attenuate the virulence of the bacilli so that inoculations with these produced a mild form of the disease which rendered the inoculated animals immune to the fatal disease. The description of Pasteur's work on the disease as given in the account of his life by his son-in-law is fascinating. Hides and wool taken from dead animals invariably contained the spores which could pass unharmed through some of the curing processes, and were responsible for some of the cases in man.
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