42 THE PROTEINS. [cH. II. 



E. The heat coagulation of albumins and globulins. 



These proteins are placed in a class by themselves, 

 because they exhibit most characteristically the phenome- 

 non of heat coagulation. 



A proper understanding of the conditions governing 

 this phenomenon is so important that students are urged 

 to study them attentively. The following matter should 

 be re-read after the section on metaproteins has been 

 studied. 



When a solution of albumin or globulin is heated under 

 certain conditions the protein separates in a form which is 

 insoluble in water, dilute salt solutions, acids and alkalies. 

 This is the phenomenon known as " heat coagulation." 

 The term " coagulation " is used as an indication of an 

 irreversible change and to distinguish the condition of the 

 protein from that of " precipitation/' in which re-solution 

 can be brought about by a change of reaction, salt content, 

 etc. 



The two most important conditions affecting heat 

 coagulation are reaction and salt content. It will be found 

 later that albumins and globulins are readily converted into 

 metaproteins by treatment with acids or alkalies, the con- 

 version being much accelerated by a rise in temperature. 

 The metaproteins are soluble in dilute acids or alkalies, but 

 are insoluble in the neutral condition, i.e. in water or 

 neutral salt solutions. An important fact about them is 

 that if a precipitate of metaprotein is boiled it is " coagu- 

 lated," that is, it will not redissolve in dilute acids or 

 alkalies. The conversion of albumin or globulin into meta- 

 protein is called " denaturation," and is a necessary ante- 

 cedent of heat coagulation. This process is best regarded 

 as an hydrolysis, which takes place at all reactions, but 

 most rapidly in either acid or alkaline solutions. At boil- 

 ing point the change is practically instantaneous, no matter 

 what the reaction may be. Should the reaction be at the 

 iso-electric point of the denaturised protein either the whole or 



