

1906.] The Chemistry of Globulin. 137 



possible molecular mass for globulin about 3000. This result will be used in 

 Section 6. 



We shall now discuss the precipitation by acids of globulin dissolved 

 in neutral salts. This is a very characteristic point in the chemistry of 

 globulin. While a little acid dissolves globulin, it precipitates it from 

 solution in salts. One would expect a priori from the similarity of salts and 

 acids that they would help one another in dissolving globulin. Instead 

 of that they are antagonistic. Hardy has shown that the solvent power of 

 two neutral salts for globulin is the sum of their separate powers. All the 

 more striking, therefore, is the antagonism of neutral salts and acids. It 

 seems to me that the explanation of this fact is to be found in this, that the 

 acids enter into the globulin molecule in different places from the neutral 

 salts, because the H atom can play a different role, in organic compounds from 

 that possible to metallic atoms. The ordinary organic compounds are far more 

 stable than the organo-metallic. 



Moreover, the molecule of acid and of neutral salt enter the globulin not 

 only in different places, but in places which make them incompatible with 

 one another, unless special provision is made to keep them in position. Each 

 is stable in its own place. Together they tend to instability. Hence, acids 

 and neutral salts inhibit one another's action in dissolving globulin. We can 

 apply this idea quantitatively to Mellanby's experiments in which acid is 

 made first to precipitate globulin from solution in salts, and tnen to redissolve 

 the precipitate. He used his solutions in such a way that the total amount 

 of globulin and of neutral salt in the 10 c.c. of mixture under observation 

 remained constant in a set of experiments. The strength of the neutral 

 salts was 0*005, or 0'003 gramme per cubic centimetre, and of the globulin 

 sufficient to saturate the salts. The amount of acid present in any case in the 

 10 c.c. is specified by the number of cubic centimetres of N/100 acid from 

 which it could be obtained. The results show that up to maximal precipita- 

 tion the fraction of the globulin precipitated is practically proportional to the 

 amount of acid present. In fact, Mellanby's graphs, in which p the fraction of 

 globulin precipitated is ordinate and amount of acid is abscissa, could be 

 replaced by two straight lines, one running up from the origin to the point 

 of maximum precipitation, and the other running down again to a point of 

 zero precipitation or complete solution. 



-To discuss the theory of the whole action, let us denote by a the cubic 

 centimetres of acid which in the absence of salt would just dissolve all the 

 globulin. Let o be the number producing maximal precipitation in a given 

 salt solution containing the globulin. Then b would dissolve the fraction b/a 

 of the globulin in the absence of salt. But the salt present is able just 



M 2 



