The Coagulation of Protein by Sunlight. 



247 



regulated only one will take place. Thus it is possible to remove the water of 

 solution or solvate water from the colloidal particles by means of 95 per cent, 

 alcohol in the cold. Flocculation is thus brought about, as is the case by 

 concentrated salt solutions, which is reversible and not accompanied by the 

 change called denaturation. If, however, alcohol be added to a protein solution 

 in like manner, but at 30° C, then the power of alcohol as a dehydrating 

 agent appears so augmented that not only does it remove solvate water, but 

 also may be pictured as inducing internal anhydride formation (denaturation). 

 The precipitate thrown down is irreversible. In the case of mechanical 

 coagulation, the phenomenon is much more readily produced if a dehydrating 

 agent is present in quantity. It would be interesting to know if it would 

 occur at all should every trace of electrolyte be removed from the solution. 



From the above discussion, it would appear that the role of light as a 

 coagulating or denaturating agent is similar to that of heat — a catalyst of 

 the primary fundamental chemical reaction. That certain substances can aid 

 or hinder its action is very probable from preliminary observations. Certain 

 it is, from the results of Experiments 3 and 4, that serum albumin is many 

 times more sensitive to light than ovalbumin. In this connection, it is 

 interesting to note that the purest serum albumin solutions still contained a 

 minute amount of pigment. I am unable to say whether the greater 

 sensitivity of serum albumin was or was not due to its influence. 



Summary. 



Serum albumin and ovalbumin which have been several times recrystal- 

 lised become sensitive to intense light, either sunlight or strong arc illumina- 

 tion, from which the infra-red and ultra-violet rays have been removed. 

 Serum albumin is many times more easily affected than ovalbumin. 



The change brought about by light has many of the characteristics of heat 

 coagulation. It consists of two separate reactions : (1) denaturation — a 

 primary chemical change ; (2) flocculation — the precipitation of denatured 

 particles. 



The primary reaction is accompanied by increase of viscosity and optical 

 rotatory power, and decrease of surface tension. The velocity of the primary 

 change is increased both by acids and by alkalies. During the reaction, 

 H ions are removed if the Ph be on the acid side of the isoelectric point ; if 

 on the alkaline side, OH ions are removed. 



The secondary reaction does not follow if the solution be free from 

 electrolytes. It is brought about by adjusting the solution to about the 

 isoelectric point of the albumin, P H 4 - 8-5 , 4. Under conditions when the 

 precipitate is formed readily, it will go back into solution on the addition of 



