and to be unalterable; the air of towns, of theatres, of large heated apartments, crowded with people, was boldly asserted by chemists still alive to be eudiometrically perfect. [63] There were no medical men in Rome for the first five centuries of her great career; and some have fancied that this fact explains the astonishing number of armies which the republic found no difficulty in sending into the field. [64] When unassisted by other deleterious influences, the poison, though all but universal over the locality, may not be destructive. After the draining the Lake of Haarlem, the principal physician of the district informed me that in 2000 cases of ague he had not lost a patient. [65] The choleraic ferment traversed in ships, no doubt, the Atlantic, as typhus had often done before; but there are grounds for believing that vegetable and animal matters in a state of rottenness (fermentation), floating about in the air, are not unfrequently transported to great and almost incredible distances. Ehrenberg and Humboldt have particularly insisted on this fact, and have spoken of distances traversed by these fermentable elements, which I hesitate to quote from memory. Assuredly they were very great, extending to some hundred miles from the seat of their origin. § 1. _Discovery of foreign bodies, the remains of animal and vegetable life, and therefore_ FERMENTABLE, _in the air floating over canals, ditches, marshes, &c._--Scientific chemists, as well as the professors of the conjectural art, are occasionally behind the knowledge of the careful, observing, unprejudiced practical men of the day.[66] Experience taught me, whilst engaged in other inquiries, that the sulphuretted hydrogen gas arising from the waters of the canals of Holland is quite sufficient to spoil cottons printed with nitrate of lead, used for dyeing yellow with the chromate of potass. The waters of these canals hold this gas in solution in a certain sense, but from May to September inclusive, the gas escapes during the night in great abundance. [66] England has often paid a high price for the first steps in science. Mr. Papillion, in 1806, received from Government 10,000_l._ for the introduction of dyeing Turkey red; and his success was owing to his knowledge of the water proper for the operation, which must be void of fermentable bodies. At this time vapours arising from the waters and floating over the adjoining grounds, were found to contain minute portions of aquatic plants mingled with the spores of fungi in vast abundance, together with fragments of a membranous and gelatinous substance about to be mentioned. To these must be added the remains of infusoria not to be detected in dried specimens.