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of them, a very small number of persons suffice to apply them. To be really useful in the council, it is necessary to have an extended knowledge of natural philosophy, of the constitution of the soil on which the state or city stands, and of the geology of neighboring regions; it is necessary, above all, to know with exactness the action which trades may have on the health of those who exercise them, and the much more important action of manufactories of every species on plants, on men congregated in towns, and on animals. This knowledge, so important, of the action of trades and manufactories, is not to be acquired by ordinary study, or in the silence of the cabinet. It is not to be obtained without positive notions on the arts, and on the greater part of the processes peculiar to each trade. It requires habit, and the frequenting of the places of work. In this particular, more even than in medicine, books are not a substitute for practice ; and, if there exist works on this subject, they are more likely to mislead than enlighten.
“From what has been said, the necessity will be evident, to introduce into the council those physicians who have made health, and particularly the public health, a special study ; and to join with them chemists, and, above all, manufacturing chemists : because what would many of those persons, whose life has been passed in hospitals and the exclusive study of medicine, be before a steam-engine ? It is clear that