W. J. V. OSTERHOUT 417 



This formula is based upon the assumption that the electrical 

 resistance is proportional to a substance, M, which is formed and 

 decomposed by the reactions^ 



We assume that when the tissue is transferred from sea water to 

 NaCl, or to CaCl2, or to a mixture of these two solutions, the reactions 

 —^ S -^ A cease, while the reactions A —^ M —^ B continue. By 

 assuming various values of Ka (the velocity constant of the reaction 

 A — > M) and of Km (the velocity constant of the reaction M -^ B), 

 and employing these in the formula, we obtain curves which closely 

 approximate those which we find by experiment. The values of the 

 velocity constants which are thus obtained are given in Table II. 



It is evident from Table II that as the per cent of CaCl2 in the mix- 

 tures increases (beginning at 1.41 per cent CaCl2) the value of Km 

 first falls and then rises, its minimum value occurring in 97.56 NaCl 

 + 2.44 CaCh (which is the mixture in which the tissue lives the 

 longest). It seems reasonable to assume that in each mixture a sub- 

 stance is formed which reduces the value of Km. We may assume 

 that the decrease of Km is directly proportional to the amount of 

 this substance, which may be assumed to occur in maximum amount 

 in 97.56 NaCl + 2.44 CaCl2. 



The simplest assumption which we can make is that NaCl and 

 CaCle combine with some constituent of the protoplasm, as XZ2, to 

 form a compound.^ If we suppose that the compound is Na4XCa, 

 formed by the reversible reaction 



4 NaCl + XZ2 + CaCU ;:^ Na4XCa + 2 ZCI3 



we can calculate the amount of Na4XCa which is formed in each 

 mixture of NaCl and CaCl2. 



2 per cent CaCl2 are omitted, as it was subsequently found that this solution con- 

 tained more than 2 per cent CaCl2. 



For the data concerned and for the derivation of the formula see Osterhout, 

 W. J. v., Proc. Am. Phil. Soc, 1916, Iv, 533. In the present paper the formula 

 previously used is multiplied by 305 and 10 is added. 



^ These are regarded as monomolecular and irreversible or practically so. 



*It is assumed that XZ2, Na4XCa, and ZCI3 are in solution. Since the per 

 cent of XZ2 which is transformed to Na4XCa is negligible, the concentration of 

 XZ2 may be regarded as constant. 



