32 THE ALBUMINS. 



such bodies do not occur in a state of actual solution. This, how- 

 ever, is not necessarily the case, and it is more likely that their 

 inability to pass through animal membranes is to be explained bv 

 the great size of their molecule. This property of the albumins is 

 very important, as it enables us to separate these bodies from a large 

 number of other substances which may be present in the same solu- 

 tion, and to some extent also from each other. 



Coagulation. It has just been stated that according to Graham's 

 view the albumins do not occur in a state of actual solution. While 

 this may be questionable, we know nevertheless that solutions of 

 these substances are quite unstable and possess a marked tendency 

 to revert to the solid state. In this respect also they behave verv 

 much like the inorganic colloids. Thus, when a solution of sodium 

 silicate is added to a large excess of dilute hydrochloric acid the 

 silicic acid which is thus formed is apparently held in solution. If 

 then the excess of hydrochloric acid, together with the sodium 

 chloride which was formed during the reaction, are removed by 

 dialysis, an apparently clear solution of silicic acid remains in the 

 dialyzer. This, however, is at once transformed into a thick, gelat- 

 inous mass w r hen a small amount of carbonic acid is passed 

 through the solution. Some of the albumins, such as the globu- 

 lins, behave in much the same manner. In undergoing such 

 changes the albumins may retain their original properties and 

 structure, or they may be altered in such a manner that they are no 

 longer soluble in the original neutral media. Then they are said to 

 be coagulated. 



The phenomenon of coagulation is common to all true albumins, 

 and upon this property the ability of certain forms to occur in a 

 more or less solid state in the tissues of the body is no doubt 

 dependent. With this statement, however, I do not wish to convey 

 the idea that the albumins which go to form the groundwork of such 

 structures as connective tissue, cartilage, and the like, occur in a 

 state of actual coagulation, analogous to that which can be brought 

 about through the influence of heat, The phenomenon simply indi- 

 cates the direction which we shall have to follow in seeking for an 

 explanation of the occurrence in the tissues of living animals of cer- 

 tain albumins, in the solid or semisolid state. 



In certain groups of albumins, such as the albumins proper and 

 the globulins, coagulation is brought about in the most characteristic 

 manner through the influence of heat, providing that the solution 

 presents a neutral, or, better, a feebly acid reaction. If the reaction 

 is alkaline, coagulation is not complete, and in the presence of a 

 certain amount of free alkali or an alkaline carbonate it may not 

 occur. An excess of organic acids similarly prevents coagulation, 

 and care is therefore necessary to insure only a feebly acid reac- 

 tion when it is desired to free a solution from all its coagulable 

 albumins 



As the temperature at which coagulation of the various albumins 



