98 A. P. MATHEWS 



The protoplasmic system is made up of masses of proteid matter 

 in equilibrium apparently with particles of the same proteid in solution. 

 It may be regarded as a two-phase colloidal system. We may assume, 

 in the light of the investigations of the past five years, that changes in 

 the protoplasmic activity are due, in part at least, to changes in the 

 state of these colloidal particles and masses, and that the salts are 

 affecting vital processes in part by producing such changes. What 

 we have to compare, then, in the first instance, is the potential of the 

 energy of the protoplasmic colloids with the potential of the potential 

 energy of the ions of the salt solution. We have, therefore, to get a 

 clear idea of the relationship of salts to the precipitation and solution 

 of colloids. 



Since the protoplasmic colloids are for the most part composed of 

 albumin in combination with other radicles, it is to the albuminous or 

 proteid colloids to which attention may first be directed. The work 

 of Kossel and Fischer has cleared up the structure of the albumin 

 molecule, which has been shown to be a polymer of amino acids. As 

 a result, albumin or proteid is shown to be both acid and basic ; that is, 

 it is capable of uniting with metals to form true salts, and also with 

 acids through the amino group. 



If common egg albumin is dissolved in alkaline solution, it exists 

 as sodium albuminate; if it is dissolved in hydrochloric acid, it 

 exists as albumin chloride. Sodium albuminate dissociates electro- 

 lytically, owing to the high dissociating power of sodium (that is, its 



high solution tension), and Na + and albumin ions are formed. Simi- 

 larly, owing to the high dissociating power of the chlorine, albumin 



+ 



chloride dissociates into albumin and Cl ions. This dissociation 

 results in giving the albumin that is, the colloidal particle a positive 

 or negative electric charge. It is possible to change the sign of the 

 charge on the albumin particles by making an alkaline solution suffi- 

 ciently acid. This is brought about in the following way : By adding 

 acid to the alkaline albumin the highly dissociated sodium compound 

 is replaced by the slightly dissociated hydrogen compound. The 

 result of this is that the charge on the colloid is neutralized, undis- 

 sociated albumin is formed, and if the concentration of the albumin is 

 sufficiently great, precipitation will occur. If one continues to add 



