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The sixth and seventh chapters are new. Spin'a brought his history down only to the time just pre ceding Koch's experiments. These two chapters con tain an account of the investigations Of Koch and of the various subsequent experiments of other Investi gators, and their attempts to verify or to overthrow his conclusions. They include a full description of the latest experiments Of Dr. Spina, in which he claims to have disproved Koch's theories. A Sketch of Koch's reply to Spina is given also.
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