SEBUM 193 



Render A faintly acid with a drop of 2-per-cent. acetic acid, and heat in a 

 test-tube. The temperature of the test-tube may be raised by placing it in 

 a flask of water gradually heated over a flame. A thermometer is placed in 

 the test-tube, and should be kept moving so as to ensure that all parts of the 

 liquid are at the same temperature. The quantity of liquid in the test-tube 

 should be just sufficient to cover the bulb of the thermometer. A flocculent 

 precipitate of coagulated serum globulin separates out at about 75. 



Now take the filtrate B. This contains the serum albumin. Dilute it 

 with an equal volume of water ; render it faintly acid as before, testing the 

 reaction with litmus paper. Heat. A flocculent precipitate (a) falls at about 

 73 C. ; filter this off; note that the filtrate is less acid than that from 

 which the precipitate has separated, or it may even be alkaline. If so, make 

 it faintly acid again, and heat; a precipitate falls at 77-79 C. (/3). A third 

 precipitate is similarly obtained at 84-86 C. (7). In the serum of the ox, 

 sheep, and horse the a precipitate is absent : in cold-blooded animals, the /3 

 and y varieties are absent. 



3. Take a fresh portion of B, and saturate it with sodium sulphate. The 

 serum albumin is precipitated (completely after a long shaking). This is 

 due to the formation of sodio-magnesium sulphate. B was already saturated 

 with magnesium sulphate (MgS0 4 + 7H 2 O) ; on adding sodium sulphate a 

 double salt (MgS0 4 .Na.,S0 4 + 6H 2 O) is formed. Shake some serum with 

 sodium sulphate alone. A small precipitate of globulin is produced. 1 Saturate 

 another portion of the serum with sodio-rnagnesium sulphate ; both globulin 

 and albumin are precipitated. 



Of the methods used for precipitating serum globulin practically only two 

 are used now. There are Haimnarsten's and Kauder's. The other methods 

 only precipitate the globulin incompletely. Kauder's method is rapid and 

 efficacious : if the globulin is filtered off, the albumin may be precipitated in 

 the nitrate by complete saturation with the same salt, ammonium sulphate. 

 This method avoids the trouble of using two salts as described under 3. This 

 last method is instructive, but not nearly so quick as Kauder's. 



With regard to the separation of serum albumin into a, /3, and y varieties 

 by the use of the method of fractional heat coagulation, it must be men- 

 tioned that at present no further difference has been shown to exist between 

 them, and the opinion has been very freely expressed that the results 

 obtained are not trustworthy. I am convinced that the method is a good one, 

 especially as in other cases (see MUSCLE) the proteins so separated can be 

 shown to possess other differences. In the case of serum, however and the 

 same is true for egg albumin the matter must still be considered subjudice. 



Kecent research has shown that serum globulin is not a single protein. 

 We have already seen that the precipitation which occurs by means of 

 dialysis is incomplete. It has now been shown that serum globulin as 

 ' salted out ' by means of the sulphate of magnesium or ammonium really 

 consists of two proteins ; one of these (en-globulin) is precipitable by dialysis : 

 the other (pseudo-globulin) is not. 



1 That is at room temperature ; if the temperature is raised to 36 C. sodium 

 sulphate acts like ammonium sulphate and precipitates all the proteins, except 

 peptone. 







