82 CHEMICAL STATICS 



frequently either insoluble or of a different color from the free 

 indicator or its combination with inorganic acids or bases (27) 

 (17) (36). 



10. The Method of "Masking" the Physiological Effects of 

 Ions by the Addition of Proteins to their Solutions. — This 

 method although, as yet, only of qualitative importance, is 

 nevertheless of surpassing interest to the physiologist, since the 

 fluids which bathe the tissues contain notable quantities of 

 protein, which may be supposed to modify, in a greater or less 

 degree, the physiological action of the inorganic substances 

 which they contain. This method appears to have first been 

 employed by Loeb (24), and it has since been utilized by Stiles 

 and Beers (50) who, among other observations, have shown that 

 the onset of rigor, which rapidly occurs when frogs' muscles are 

 immersed in solutions of barium salts, is greatly delayed when 

 protein is added to the solutions. These experiments are, how- 

 ever, not conclusive since they are open to the criticism that the 

 added protein may alter the permeability of the tissue for inor- 

 ganic ions, for example, by clogging up the pores of the external 

 limiting membranes. This criticism, although a serious one from 

 the chemical standpoint, does not, however, detract from the 

 interest to physiologists of such experiments, since, whatever the 

 mechanism may be which leads to modification by proteins of 

 the physiological effects of inorganic substances in solution, the 

 probable importance of such effects in life-phenomena is the 

 same. 



La Franca (21) has published the results of a series of experi- 

 ments which, in the light of the important investigations of 

 Madsen and Nyman (26) hold out the hope that this method 

 may ultimately be employed in a quantitative manner. This 

 observer, employing the method of Paul and Kronig (20) (32), 

 determined the toxicity, for bacteria, of solutions of copper 

 sulphate, mercurous nitrate and silver nitrate to which varying 

 amounts of protein had been added; at the same time he meas- 

 ured the concentration of heavy-metal ions in the solution by 

 the potentiometric method. His results show a satisfactory 

 parallelism between the diminution in the toxicities of these 

 solutions caused by the addition of the protein, and the number 

 of heavy-metal ions bound by the protein, as revealed by the 

 potentiometric measurements. 



