1. Fibrin clots prepared in the absence of calcium can be dissolved in solutions of lithium chloride and bromide and sodium bromide and iodide, as well as of guanidine hydrochloride and urea. These salts do not denature fibrinogen under the same conditions of concentration, temperature, and time. Sedimentation experiments on the fibrin solutions show in each case a single sharp peak with a sedimentation constant close to that of fibrinogen.
2. At lower concentrations, these salts inhibit the clotting of fibrinogen by thrombin, but in the case of lithium bromide and sodium iodide, at least, allow an intermediate polymer to accumulate whose sedimentation constant is close to that of the polymer observed in systems inhibited by hexamethylene glycol or urea.