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ITI. The Relation of Biochemical Colloids to Electrolytes. 
We have already met with several instances in which the inter- 
action between colloids and electrolytes plays an important part. In 
the present section, further analysis of such phenomena will be 
attempted, ; 
It is necessary to take account of the fact that the greater number 
of the colloids occurring in living organisms are proteins. These, 
being conjugated amino-acids, behave as amphoteric electrolytes, able 
to combine with strong acids by their NH» groups and with strong 
bases by their carboxyl groups. Electrolytically dissociated salts are 
thus formed, the protein ion being the cation in the former case, the 
anion in the latter. Although there is no doubt of this fact, it is 
sometimes forgotten that the protein itself is present in solution in 
the form of an anhydride, the NH», and CUOU groups are not free to 
combine with ions until hydrolyzed by the actiun of strong acids or 
bases. Nevertheless, various statements have been made to the effect 
that not only are chemical compounds formed with weak acids, but 
even with neutral salts. That this is not so is shown clearly by the 
results of Bugarsky and Liebermann (1898), who found no change in 
the freezing point on adding egg albumin to sodium chloride, 
whereas there was a marked depression with hydrochloric acid or 
sodium hydroxide. The evidence brought by Pfeiffer and Modelski 
(1912), to the effect that amino-acids form definite chemical com- 
pounds with calcium and lithium chlorides and other salts, is not 
convincing and the present writer was unable to confirm their 
statements. 
Hardy (1905-6) finds that globulins form non-ionized complexes 
with neutral salts. On the other hand, Loeb (1918) holds that 
neutral salts with a univalent cation form highly ionizable salts 
with gelatin. The evidence is that powdered gelatin, after washing 
with m/8 or m/4 solution of sodium chloride, shows a further 
swelling when afterwards put ir contact with a more dilute solution 
of a neutral salt with a univalent metal. There is a critical concen- 
tration above which this additional swelling is absent. And this 
concentration is half as great if the anion is bivalent, regardless of 
the nature of the anion and cation. The evidence is somewhat 
