We have already described briefly the portals of entry and of excretion of the pathogenic spirochetes. We may mention here that we have twice prevented epidemics by disinfection of the ground and the removal of the inundated water in certain places in coal mines. In one mine 19 out of 50 workmen, and in another 9 out of 30 workmen came down with Weil's disease in about 2 weeks.

We have already pointed out that the period during which the pathogenic spirochetes are excreted in the urine continues, as a rule, for 40 days, and that we must, therefore, apply disinfection for at least 40 days after the first appearance of the disease. Lately we have found that in 21 cases out of 24 the spirochetes were excreted in the urine for 40 days, in one case until the 42nd day, in one case until the 45th day, and in still another case until the 63rd day.

Another important fact concerning the prophylaxis which has been brought out is that both house and ditch rats (brown) carry virulent Spirochæta icterohamorrhagæ, the causal spirochete of Weil's disease, in their kidneys. Miyajima has reported that field rats have the pathogenic organisms in their kidneys; he will report these findings in detail later. The spirochetes which he described are less virulent than ours. On his advice we have carefully examined house and ditch rats in the city and rats in the coal mines of Kyushu, where Weil's disease prevails, and found that 39.5 per cent carried highly virulent pathogenic spirochetes in their kidneys, thus confirming Miyajima's experiments. The kidneys were examined microscopically under the dark-field microscope, and in the cases in which we did not find the pathogenic spirochete, we made inoculations into guinea pigs. Thus we found Spirochæta icterohæmorrhagiæ microscopically in the kidneys or in the urine in 32.4 per cent, and by means of inoculation in 7 per cent, making a total of 39.5 per cent carrying the pathogenic organisms, out of a total number of 86 rats examined. In some instances, rats were made to bite guinea pigs and in two instances caused Weil's disease. Among fifty-five patients in our clinic, twelve were cooks; and in Europe many cases arise among butchers—indicating the relation of the disease to rats. Moreover, during the present year we observed two patients who acquired Weil's disease, one in 1 week, the other 8 to 9 days after they had been bitten by rats. These facts point to a relation between Weil's disease and rats. The infection is transmitted probably from rats to man by means of the urine of the rats, directly or indirectly. On the injection of 0.1 gm. of rat urine which contains Spirochæta icterohæmorrhagiæ into the peritoneal cavity of guinea pigs, the infection arises, while the injection of the liver or the blood of the rats into guinea pigs does not produce the typical disease.

The finding that the kidneys of rats contain the pathogenic organisms of the disease is important from the point of view of prophylaxis. The large number of rats in the trenches of the European battle-fields suggests the possibility that many cases of Weil's disease may arise. We shall report on this point in more detail later.

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