characteristics. 2. In the whole calcareous series,—which begins in the oldest mountains of our earth, proceeds through all periods, is of the greatest magnitude in those of the latest formation, presents in the petrifactions the relics of an extinct animalization, and is connected as a living member (in the coral-banks), with the existing animal world,—nitrogen and hydrogen (the essential elements of the animal world) are the principal characteristics.
The connexion between inorganic and organic life, however, is shown more immediately and more clearly in the production of organisms from pure water; to which we must refer both the origin of the Infusoria obtained by the pouring of water over mineral substances, as observed by Gruithuisen, and still more, the origin of the so-called green matter, the history of which has been so admirably traced by Priestley and Ingenhousz. These show more than all other experiments, that in the purest water, under the free influence of air, light, and heat, beings are formed which, oscillating as it were between the animal and the plant, exhibit the primitive germs of both kingdoms. The succession of the changes which take place in the formation of the Infusoria is of such importance that we cannot avoid considering them more in detail, and therefore select from the acute G. R. Treviranus[1] the following passage in reference to those cases.
"If we expose spring water[2] to the sun in open, or even in closed but transparent vessels, after a few days bubbles rise from the bottom, or from the sides of the vessel, and a green crust is formed at the same time. Upon observing this crust through a microscope, we discover a mass of green particles, generally of a round or oval form, very minute, and overlaid with a transparent mucous covering, some of them moving freely, whilst others perfectly similar to these remain motionless and attached to the sides of the vessel. This motion is sometimes greater than at others. The animalcules frequently lie as if torpid, but soon recover their former activity.
"As the corpuscles constantly become more numerous, the crust increases likewise. After a few weeks the latter acquires a certain thickness and consistency. If we examine it in this state, it appears exactly as described by Priestley. It looks in fact like a slimy sediment of the water, which has become green under the influence of the sun without presenting any trace of organization. The green particles, which were visible at the time of their formation, are now so crowded together, and perhaps so changed in their organization, that the most attentive observer, unless he had closely followed their metamorphosis step by step, would hardly be able to discover the traces of their primitive form.
"A few weeks later, when the crust has assumed a still greater con-
