126 PHYSIOLOGY CHAP. 



Paraglobulin is also known as serum globulin, because it 

 remains unchanged in the serum after spontaneous blood coagula- 

 tion. It can be readily separated in the pure state by diluting 

 the serum with at least ten volumes of water, and then leading a 

 stream of carbonic acid through it, or by slightly acidifying it with 

 dilute acetic acid, or by saturating it with magnesium sulphate. 



Serum globulin dissolved in a 10 per cent solution of common 

 salt coagulates at 75 C. 



Serum albumin or serin is separated from globulins of the 

 serum by salting the latter with magnesium sulphate at 30 C., 

 filtering it at the same temperature, and adding to the saturated 

 filtrate dilute acetic acid, or ammonium, or sodium sulphate to 

 saturation. This precipitates the serum albumin : the precipitate 

 is separated by centrifuging, and purified by dialysis. 



Pure serum albumin dissolved in distilled water coagulates 

 rapidly at about 50 C. ; but on adding salts its heat-coagulability 

 is considerably lowered. In solutions of 5 per cent sodium 

 chloride, coagulation first occurs at 72-75 C. 



Serum albumin is not identical with ov-albumin, 'as appears 

 from certain chemical properties, and more particularly from the 

 physiological characteristic by which the latter, when injected into 

 the veins, is not retained in the blood, but is at once excreted by 

 the kidneys and passes unchanged into the urine. 



After Morner had isolated a protein of the m.ucinoid group 

 from white of egg, to which he gave the name of ovo-mucoid, 

 Zanetti, in Ciamician's laboratory, by a happy inspiration sought 

 to ascertain whether the same or some other analogous sub- 

 stance were not also contained in blood serum, which shows a 

 certain similarity to egg-white in its composition. His experiments 

 with ox serum were crowned with success. The new substance 

 sero-mucoid, which he discovered, exhibits physical and chemical 

 properties highly similar to those of ovo-mucoid. 



The four proteins named above are all that have at present 

 been definitely demonstrated in blood plasma. When exposed to 

 the action of freely diluted acids or alkalies, and warmed, they 

 turn into alkaline or acid albumins, the former being similar to 

 the casein of milk, the latter to syntonin. But there is no 

 evidence for the presence of these in normal blood plasma. 



The quantitative relation between fibrinogen, serum globulin, 

 and serum albumin is not easy to determine. It appears probable 

 that the relative quantity of these three proteins is very variable, 

 and that all three function as tissue-forming substances, the 

 albumin representing the true form, and the two globulins two 

 different modifications produced by cell metabolism. Miescher 

 and Burckhardt have actually shown that the globulins of the 

 blood increase during hunger, while the albumin decreases. 



The same facts and the explanation of them have been 



