The results of the study of the inhibiting effect of neutral salts upon the clotting tendency of fibrinogen by thrombin may be summarised as follows:

Salts like NaCl and KCl inhibit only weakly.

Salts of the same cation (K) with monovalent anions of different ionic radius are the more active the larger the anion (Cl',Br',I').

Salts of the same cation with anions of different valency are the more active the higher the charge of the anion (1–1 <1–2 <1–3 <1–4).

Salts with the same anion with cations of different valency show stronger inhibition in the case of cations of higher charge (K,Na < Mg••, Ca••, Sr••, Ba••).

Salts with the same anion and cations of the same charge, but of different radius, are the more active the larger the cation (but with an inversion between Mg•• and Ca•• in the series of the alkali earths, which is not infrequent in biocolloids).

These results show that the clotting of fibrinogen with thrombin is, at least partly, caused by a coacervation process, due to electrostatic attraction between positive and negative groups. Its nature and localisation will be dealt with in the next paper of this series.

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