affect an electrostatic repulsion dependent upon the charge density of the complexing anion. In order to conform to the observation that increasing the ionic strength of the same salt does not affect the energy of activation, we would have to postulate that these sites are fully saturated at low salt concentrations.The following scheme is the summary of the proposed mechanism of collagen formation and its reversal T -*• T* Collagen where T is tropocollagen, ', the inactive form and T*, the proposed intermediate that is being formed during the lag period. ' is formed when active sites on tropocollagen are blocked by anions, cations or by such agents as urea.Conditions which enhance hydrogen bonding favor the formation of collagen, while those which rupture hydrogen bonds reverse the equilibrium. The equilibrium rate will be influenced by pH, type and ionic strength of the salt present, concentration of the protein and temperature. Thus, when the collagen solution is removed from the presence of the fiber and conditions are adjusted to favor collagen formation, the system will remain poised unless conditions also favor a reasonable rate of reaction.In writing this paper, we have avoided the use of such terms as neutral-soluble or acid-soluble collagen. The impressions gained from this work have cast considerable doubt in our minds as to whether such differences really exist. It must be realized that when HO Ac solutions of collagen are adjusted to values above pH 7, the optimum pH of fiber formation is being approached. If the other variables are such as to favor coagulation, fiber formation will occur.If not, a collagen solution which is soluble in neutral or alkaline solutions will be obtained. We have found that after coagulation, the fibers can be redissolved in HO Ac, the collagen reneutralized, and fibril formation repeated as before.

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b Infrared absorption spectra are described characterizing the 3-phenyl-2-thiohydantoins, the 3-(phenyl-p-azophenyl)-2-thiohydantoins, and the 3-0-nitrophenyl-2-thiohydantoins of amino acids. The spectra of some preparations deviate from the characteristic phenylthiohydantoin absorption pattern. For these compounds the openchain thiocarbamyl structure is assumed. The spectra are highly characteristic and serve to identify the amino acids from which they are derived.

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