82 COLLOIDS, IN BIOLOGY AND MEDICINE 



We encounter such lyotropic series regularly in the salting out of 

 hydrophil ecolloids (see Albumin, p. 146 et seq., Lecithin, p. 140, 

 Gelatin, p. 161) and in many biological phenomena, where they tend 

 to cause either a precipitation or a concentration. 



However, we must not assume that the action is such that in one 

 case the anion alone is active, and in the other the cation alone. 

 There are many reasons for believing that there is an antagonism 

 between anions and cations, and that the action of the cation is more 

 or less powerfully increased or diminished depending upon the 

 anions present. If in a given instance we speak of the cations 

 causing precipitation or dehydration, we always mean the difference 

 between the effect of the cation and the opposed action of the anion 

 present, in which, however, the action of the cation predominates. 



The divalent cations Mg, Ca, Sr and Ba act more strongly as pre- 

 cipitants than the monovalent cations. Biologically they are im- 

 portant in connection with alkali salts, inasmuch as small quantities 

 of calcium Baits are able to replace considerably larger quantities of 

 alkali salts, e.g., Na or K. This greater effect may even lead to an 

 antagonism between the two; it has been thoroughly studied by 

 Wo. PAULI and H. HANDOVSKY.* 3 It is sufficient to mention 

 that in the case of alkali albumin, Ca salts form a less ionized 

 Ca albumin combination from a more ionized Na albumin combi- 

 nation. According to the law of mass action small quantities of Ca 

 may be replaced by larger quantities of Na. We may thus under- 

 stand the significance of the Ca content in all physiological fluids. 

 Mg, Sr and Ba act in a similar manner. They have in addition 

 certain specific properties which obscure the relations. 



Large quantities of alkaline earths cause irreversible changes in 

 many biocolloids, that is, they produce insoluble compounds with 

 them. Electrolytes may exert another effect on the biocolloids; 

 they may cause "flocculation," a phenomenon we shall now study 

 more closely. 



Flocculation. 



If albumin is boiled, it coagulates. A coagulation of albumin may 

 also be produced by the addition of ammonium sulphate. Though 

 the latter process may be reversed by dilution with water, the boiled 

 albumin cannot again be brought to its fluid condition, by any 

 physical means. The hydrophile colloid has been converted into a 

 hydrophobe colloid. For uniformity's sake, we shall consider as co- 

 agulations only such processes as cause an irreversible change. 



If we heat a very dilute albumin solution, there is apparently no 

 coagulation; at most the fluid becomes slightly opalescent. In 



