§ 3. It may be now fully admitted that ammonia is the active principle or stimulus to vegetable life, as shown by the extraordinary growth of plants in warm damp climates; in these malaria--as we may still call the poison so developed--exists to the greatest extent, as in the Pontine Marshes, by the banks of the Po, Ferrara and Bologna. From various experiments and observations, I have been led to the conclusion that the ammonia constantly present in the atmosphere, and derived from several sources,[67] is the chief cause of the activity which the ferment, or poison, displays under different and varying circumstances. There prevails, in truth, an excess of ammonia in such an atmosphere, resulting from the nitrogen uniting with hydrogen; from the decomposition of vegetable matter carrying decayed animal matter along with it; and from the ammonia always existing in the spawn and in the matter of the shells of infusoria. All my researches into the effects which the various gases have upon animal tissues, showed ammonia to be the most destructive; in fact, no animal tissue can resist complete decomposition by caustic ammonia. I conclude, therefore, that vegetable and animal matter in a state of fermentation, and mixed with ammonia, is the cause or essence of that destructive power which physicians ascribe to malaria. Should this fermentable matter pass in a concentrated state into the torrent of the circulation, the globules of the blood are destroyed, and become black; the person is in the cold stage of fever; next, the vegetable matter ferments, causing the hot stage. No one in Holland has any doubt as to the origin of this power, but ascribes it uniformly to the draining of some lake; and it amounts almost to a demonstration that the air under such circumstances is poisonous or injurious to health. It was even foretold by several writers that fevers would result from draining the lake of Haarlem, as took place in the years 1608, 1641, 1727, 1779, from draining various polders.[68] [67] The ammonia always present in the atmosphere is probably derived chiefly from the union of nitrogen and hydrogen; but much of it also no doubt has its source in the fermentation of animal and vegetable remains. [68] Baron von Lynden.