Loeb,[52] working with Gonionemus, and with the striated muscles of the frog, arrived at conclusions which are in some respects entirely opposed to those of Howell. What Loeb spoke of as the toxic effects of sodium chloride was emphasized by this work. This was especially shown in the case of Fundulus eggs which, though freshly fertilized, cannot develop in pure NaCl solution, although they develop in sea-water or in distilled water. In this case the addition of a small quantity of calcium chloride to the NaCl rendered development possible. According to Loeb, the Ca exerted an antitoxic effect and neutralized the injurious action of the NaCl. Similarly it was found that the apex of the heart contracts rhythmically in a pure NaCl solution, but soon came to a standstill. The addition of a small amount of calcium is sufficient to cause the contractions to persist for a long time. This again was referred to the toxic and antitoxic effects of the salts. From these and similar experiments arose the conception of “physiologically balanced solutions” in which the toxic effect of each substance in the solution is exactly counteracted by the antitoxic effect of some other substance in the same solution. Other experiments by Loeb showed that if the voluntary muscle of a frog be immersed in a pure NaCl solution, rhythmical twitchings appear which continue for many hours, or even for days. If, however, a small quantity of CaCl_{2} be added to the NaCl solution the twitchings cease, although the muscle remains alive in this mixture longer than it does in pure NaCl. Similar results were obtained with solutions of the sodium salts which precipitate calcium, fluoride, oxalate, carbonate, phosphate, etc. In all of these solutions twitchings developed in the muscle. Magnesium and strontium act like calcium in inhibiting the muscular twitchings produced by sodium salts. These experiments led Loeb to the conclusion that the presence of calcium in the body keeps the voluntary muscles from constantly twitching or beating rhythmically in the way the heart does. Calcium, magnesium, and strontium seemed to have a definite inhibitory action on the muscular contractions. Loeb further showed that the center of a jellyfish (Gonionemus), which when isolated from the margin will not contract in sea-water, will beat rhythmically if placed in pure NaCl solution. If a quantity of CaCl_{2} or Ca(NO_{3})_{2} be added to the NaCl solution the contractions are inhibited. Magnesium and strontium behave in this respect like calcium. If also a sufficient quantity of a calcium precipitating solution (sodium fluoride, phosphate, etc.) be added to sea-water in which the center will not beat, rhythmical contractions soon appear, due apparently to the removal of the calcium from the sea-water and the tissue. In these experiments, as in those with voluntary muscles, calcium, magnesium and strontium have apparently an inhibiting action on muscular contractions.