. General physiology; an outline of the science of life. THE GENERAL CONDITIONS OF LIFE 281 and decreases with the rise and fall of the water-contents. If a slight shower of rain comes, activity immediately begins, the plants grow and bloom, and the sluggish animals awake from their summer sleep. In a manner somewhat different from that of the desert-plants and animals, other organisms which at times are obliged to undergo a lack of water are adapted to life in drought, since at such times they assume a quiescent phase and are protected against drying. Such quiescent phases occur especially am
. General physiology; an outline of the science of life. THE GENERAL CONDITIONS OF LIFE 281 and decreases with the rise and fall of the water-contents. If a slight shower of rain comes, activity immediately begins, the plants grow and bloom, and the sluggish animals awake from their summer sleep. In a manner somewhat different from that of the desert-plants and animals, other organisms which at times are obliged to undergo a lack of water are adapted to life in drought, since at such times they assume a quiescent phase and are protected against drying. Such quiescent phases occur especially among unicellular organ- isms, as in the spores of Bacteria (Fig. 128) or the cysts Rhizopoda and Infusoria (Fig. 84, p. 205), which enclose the living cell-substance in a thick, completely impervious Fig. 128.—Bacillus butyrlcus, forming spores, rt, Beginning of the process; h^ rijDe spores still within the bacilli; c, spores after the dissolution of the membrane of the mother-cells; d, spores beginning to germinate and to allow the bacilli to come forth. (After Migula.) The seeds of plants likewise belong to these permanent conditions of organisms. But in all these cases life is latent; no trace of vital phenomena can be demonstrated in them by means of the most delicate methods. It would appear that in all such cases life stands still, like a wound-up clock that has been suddenly stopped. From these facts the importance of water for the maintenance of life is evident. Without water life cannot exist. With the increase and decrease of the water-contents of living substance within certain limits the intensity of life rises, falls, and becomes zero. 3. Oxygen It was Priestley, the discoverer of oxygen, who recognised the fundamental importance of this gas for life upon the earth; by his epoch-making discovery of the gas and its properties he gave a real background to Mayow's ingenious comparison of respiration with combustion. In respiration free oxygen is taken up
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