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 specially reserved for these experiments, nor is it possible to allow the incubator to be used at the same time for bacteriological purposes.

(5) Before starting it must be ascertained that all utensils are to hand and in perfect condition.

(6) Experiments can only be carried on with good light. It is impossible to carry on more than five or six experiments at the same time with the necessary care.

(7) Before successful tests can be expected, one must not only be certain of a perfect knowledge of all the details of the method, but a thorough knowledge of their fundamental principles is most essential. It is not sufficient to know the method thoroughly, one must have a perfect command of it, and, as it were, live in it. No one is able to stain tissues perfectly for the first time, even though he be guided by the strictest directions. Even simple chemical methods require practice, and the most elementary analyses sometimes fail. Even the Kjeldahl method, which is so easily handled, requires to be thoroughly learnt. Should a failure result, no one would think of communicating it while blaming the method; he would never rest until the cause of the error was found. The statement, "We have been working in the strictest manner according to the given directions," I treat with scepticism on the basis of a rich experience. Such great offences are often 12