20 THE EQUILIBRIUM OF COLLOID AND 



system in equilibrium regarding ions with its surrounding medium, 

 and the equilibrium is maintained by the pressure of each parti- 

 cular ion, acting independently, in the surrounding medium. Also 

 variations in concentration of any of the ions will cause reaction 

 and variation in the equilibrium of the whole, and may cause such 

 disturbances as will alter the distribution of other ions and soluble 

 substances, and so cause variations in the character and types of 

 reaction of the protein or bioplasm. 



Two chief factors determine the equilibrium between each ion 

 and the cell ; one of these is the concentration of the ion, the other 

 the constant of association or adsorption between the cell sub- 

 stance and the ion. This constant changes its value specifically 

 from one ion to another with a constant type of cell or bioplasm ; 

 and with the same ion kept constant varies from type of cell to 

 type of cell, so giving rise to the specific picking out of particular 

 cell types by particular ions or other bodies. 1 



In addition to these chief factors, there is some evidence that 

 certain ions can replace each other, or in other words compete for 

 the same vacant places in the protein or bioplasm. This is known 

 as the antagonistic action of drugs. Usually the ions so replacing 

 must be of the same order of valency, a monad being unable to 

 take the place of a dyad, but one dyad can replace another, and 

 especially two dyads in the same periodic group of elements are 

 interchangeable. For example, one heavy metal can take the 

 place of another, and even the paradox is arrived at that the 

 poisonous action of one of these heavy metals is decreased by the 



1 This might be put in simple mathematical form thus : if C 1 be the concentra- 

 tion of the protein or other substratum in a given cell, C-> the concentration of 

 the ion to be absorbed in the medium outside (lymph), and C 3 the concentration 

 of the substance adsorbed, then C 3 - KCjCo, where K is a constant dependent on 

 the chemical and physical affinities of ion or other substance for each other, and 

 hence having a different value when either ion or type of protein is changed. If 

 now we keep the same ion, as in the distribution of any naturally occurring ion 

 in the body, or in the action of any given drug which can only be given so that 

 it is free to act on all cells in the body, then for a different cell using small letters 

 we can write as before c 3 = kciCo where the suffixes show the same meaning as 

 before. But now O a and c., the concentration of the ion or drug in the circulating 

 medium is the same in both cells, and hence if we want to get the relative con- 

 centration in the t\vo types of the cell we have ***=_ ( X and further if we take 



C 3 KC, 

 it that the protein concentration is the same in the two cells, we finally have 



- 1 3 = 7T, or the relative distribution is in proportion to the affinities between ion or 

 Lj K 



drug and particular type of protein. 



