[43] Arzneimittellehre, Leipzig, 1883.
[44] Amer. Journ. Physiol., Vol. I, 1898, p. 411.
[45] Loc. cit.
[46] Loc. cit.
[47] Amer. Journ. Physiol., Vol. X, 1904, p. 209.
[48] In all these experiments there was no interval between the emptying of the loop and the beginning of the 10-minute period which followed. The injections were made as rapidly as possible, and in no case occupied more than a minute.
CHAPTER V.
The Inhibiting Action of Calcium and Magnesium on the Movements and Secretion of the Intestine.
It was first observed by Ringer[49] that the unfavorable effect produced by pure NaCl solution could be lessened by adding other salts, notably calcium and potassium. From this observation there was made the so-called Ringer’s solution, which contains Na, K, and Ca in proportions which render the solution relatively neutral and innocuous towards the living tissues.
Howell,[50] working with the heart of the terrapin in various mixtures of Na, K, and Ca chloride, emphasized the importance of calcium in the medium in which the heart beat. He concluded from his experiments that the sodium chloride was mainly instrumental in establishing and maintaining the proper osmotic conditions, while calcium was the main factor in initiating and maintaining the beat of the heart. To quote from his articles:—“The stimulus that leads to a heart contraction is dependent upon the presence of calcium compounds in the liquids of the heart; but for rhythmic contractions and relaxations a certain proportion of potassium compounds is necessary.” “The sodium chloride seems to be essential only in preserving the osmotic relations between the tissues and the surrounding liquid.” Similar conclusions were arrived at by Green.[51]
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.