. General physiology; an outline of the science of life. STIMULI AND THEIR ACTIONS 385 Every one who has been at the sea-shore upon a quiet summer evening has observed the production of light by mechanical stimuli. The curious, transparent animal life that in quiet weather exists at the surface of the water has the wonderful power, irrespective of the classes to which the animals severally belong, of glowing brilliantly at every movement of the boat or the oars, or every dash of the waves. Where the water contains much plankton, such as Noctilucce, Radiolaria, eggs of Ctenophora, etc., the eff
. General physiology; an outline of the science of life. STIMULI AND THEIR ACTIONS 385 Every one who has been at the sea-shore upon a quiet summer evening has observed the production of light by mechanical stimuli. The curious, transparent animal life that in quiet weather exists at the surface of the water has the wonderful power, irrespective of the classes to which the animals severally belong, of glowing brilliantly at every movement of the boat or the oars, or every dash of the waves. Where the water contains much plankton, such as Noctilucce, Radiolaria, eggs of Ctenophora, etc., the effect of a shower of sparks in the water can be produced as well indoors. Every time sea-water is stirred in a glass the unicellular organisms, at the moment of the touch with a glass rod, flash up brightly, and then immediately sink again into. Fig. 177.—Carchesiuin polypinum, a branched colony of VoHicellince. A, Unstimulated ; B, stimu- lated by jarring. Tbe single individuals jerk together by the contraction of the-myoids of their stalks. darkness. The experiment can be repeated innumerable times, and the spectacle that is presented is of wondrous beauty. Before leaving the excitation-effects of mechanical stimuli, one more group deserves attention, viz., the results of rhythmically repeated shocks. Phenomena that are produced only incompletely by single shocks are expressed much more strongly by summation, providing that each succeeding impulse follows before the stimulus of the preceding one has passed away. This fact is demonstrated most distinctly in contraction-movements, where one con- traction is superimposed upon another so that there is no time for expansion to develop between them; a genuine cramp then appears, which is termed mechaniccd tetanus. The peculiarity of tetanus lies in the fact that, although composed of many single contractions, on account of their rapid succession it gives the impression of a continual process. The simplest method of producing rhythm
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