1Parts I, II and III have been published in this Journal, XLVII, p. 215, 1913, XLVIII, p. 128, 1914, and XLVIII, p. 317, 1914. A preliminary account of the present investigations was published in the Proc. of the Physiol. Soc., March, 1912, p. vii, this Journ. XLIV.