COMPOUNDS OF PROTEINS WITH OTHER PROTEINS 171 



true of the compounds of the various Protamines with such proteins as 

 casein and hemoglobin, the low proportion of protamine which is 

 present in these compounds would indicate that the protamines possess 

 molecular weights in the neighborhood of 800; much lower, that is, 

 than the weights of the majority of protein molecules. This corre- 

 sponds with their less colloidal character, the compound Salmine with 

 sulphuric acid, for example, being freely diffusible through parchment- 

 paper, and with the relatively few amino-acids they yield on hydrolysis, 

 reminding one of the peptones rather than of the more bulky and 

 complex native proteins. 



From a variety of observations it appears extremely probable that 

 many of the protein constituents which may be isolated from the 

 various tissues and tissue-fluids do not preexist there, but represent 

 fractions split off by chemical procedures from complex compounds of 

 proteins with proteins which are present in the tissue or tissue-fluid. 

 Thus W. B. Hardy has pointed out that in untreated Blood-serum no 

 proteins exist which wander in an electrical field, but. as soon as the 

 serum is acidified with acetic acid, a cloud appears, which is due 

 to partial precipitation of "Insoluble" Serum-globulin (the globulin- 

 fraction of serum which is insoluble in distilled water). On passing 

 a current through this mixture the cloud moves over to the anode. If 

 the serum be dialyzed until all of the serum-globulin has been precipi- 

 tated the remaining protein is now found to be completely ionic and is 

 precipitated, on passing a current, at the anode. Dialysis, therefore, 

 or acidification of blood-serum evidently accomplishes the detachment 

 of a fraction ("insoluble" serum-globulin) from the protein-complex 

 which preexists in untreated serum. This fraction is electrically 

 dissociated and so is the remainder from which it is split off, but the 

 original protein-complex is not dissociated at all. 



Moreover, as Hardy has also pointed out, the globulin which we 

 separate by dialysis or by acidification and dilution from blood serum 

 possesses very different physical characteristics from any which are 

 displayed by the proteins in unmodified blood-serum. In Hardy's 

 words: "The globulin-fraction has an abiding characteristic. In all 

 its solutions its molecular state is so gross as to cause the molecules to be 

 arrested by a porous pot. They will not pass such a filter even under 

 pressure. In this it is sharply distinct from the parent serum-protein, 

 which is readily filtrable. If globulin be present as such in serum it is 

 not only non-ionic, but the agent which dissolves it must be something 

 more than alkali and salt, since either alone or together they will not 

 produce so high a grade of solution." 



"The difference in the molecular grade of globulin when once 

 separated, and the electrical homogeneity of serum-protein and of the 

 fraction (still capable of further subdividion by salting-out) which 

 remains after the alkaline globulin fraction which most readily appears, 

 has been removed, suggests that serum-protein is a complex unit. If 

 such a unit exists it is not saturated with globulin. Fresh ox-serum has 



