HEAT, LIGHT AND PRESSURE 307 



oxyhsemoglobin with temperature,* that immediately prior to its 

 coagulation in the above experiments the haemoglobin existed 

 in the solution in a molecularly dispersed condition, obeying the 

 law of Avogadro. 



The high temperature-coefficient of the process explains, as 

 Chick and Martin point out, the apparent, but unreal constancy 

 of the "coagulation-temperature" which was so much insisted 

 upon by the earlier investigators quoted above. With rising 

 temperature a point is reached at which the reaction is so rapid 

 as to appear almost instantaneous. 



It is obvious that the monomolecular reaction-formula would 

 apply either to the dehydration of protein according to the formula 



H2N.R.COH.N.R.COOH = HN.R.COH.N.R.CO + H2O 



I I 



or to its hydration according to a formula of the type 

 Protein + H2O = coagulated protein, 



since in the latter case, the mass of water being very much greater 

 than that of the protein, the active mass of water would be appre- 

 ciably constant throughout the reaction. 



From the fact that dry protein, heated to high temperatures 

 does not undergo typical heat-coagulation, i.e., does not lose its 

 solubility in water (24) Chick and Martin conclude that the heat- 

 coagulation of protein is a process of hydration. From the results 

 of Pauli and myself, cited in Chap. VI, it is evident, however, 

 that the process of heat-coagulation is not one of hydration but 

 of dehydration of the protein, f according to some or all of the 

 equations (i) to (iv) in Chap. VI, section 6. From the fact that 

 the base-combining capacity of casein diminishes with rising tem- 

 perature, and also the solubility of some of the caseinates, we 

 have concluded % that with rising temperature this protein, at 

 all events, undergoes some measure of polymerization on heating 

 through the dehydration of the end — NH2 and — COOH groups 

 of adjacent molecules. § If this were a general phenomenon 



* Cf. Chap. VI. t Cf. also Michailow (56) and Starke (98). 



X Cf. Chap. VI also 1 of this chapter and T. Brailsford Robertson (83). 



§ Mann (55) states that in his opinion heat coagul tion is brought about 

 by one portion of the albumin molecule precipitating the remainder, a view 

 which is essentially similar to that expressed above. Sutherland (99) has also 

 expressed the view that coagulation of a protein is the result of polymerization 

 through the neutraUzation of "Valencies which are usually latent." 



