155 



LESSON XX 

 SEBUM 



1. The following methods of precipitating serum globulin (paraglobulin 

 should be performed : — 



(a) Fanom's Method. — Dilute serum with fifteen times its bulk of water- 

 It becomes cloudy owing to partial precipitation of the serum globulin. Add 

 a few drops of 2-per-cent. acetic acid ; the precipitate becomes more abmi- 

 dant, and it dissolves in excess of the acid. It was formerly called ' serum 

 casein.' 



(b) Alexander Schmidt's Method. — Dilute serum with twenty times its bulk 

 of water and pass a stream of carbonic acid through it. A fairly abimdant 

 precipitate of serum globulin falls. Let it settle, and an additional precipitate 

 can be obtained from the decanted liquid by treating it with a trace of acetic 

 acid (the ' serum casein ' mentioned above). Repeat the carbonic acid 

 method without dilution ; no precipitate forms. 



(c) By Dialysis. — Put some serum in a dialyser with distilled water in the 

 outer vessel. The water must be frequently changed. In order to prevent 

 decomposition a few crystals of thjTnol are added. In a day or two the salts 

 have passed out ; the proteids remain behind : of these the serum albumin 

 is still in solution ; the serum globulin is in part precipitated, as it requires 

 a small quantity of salt to hold it in solution. 



{d) By Addition of Salts : — 



(i.) Schmidt's method. Saturate some serum with sodium chloride. A 

 precipitate of serum globuUn is produced. 



(ii.) Hammarsten's method. Use magnesium sulphate instead of soditmi 

 chloride. A more abundant precipitate is produced, because this salt is a 

 more perfect precipitant of serum globulin than sodium chloride. In order 

 to obtain complete saturation with these salts it is necessary to shake the 

 mixture of salt and serum for some hours.* 



(ill.) Kauder's method. Half saturate serum with ammonitun sulphate. 

 This is done bj- adding to the serum an equal volume of saturated solution 

 of ammonium sulphate. This precipitates the globulin. Complete satiura- 

 tion with the salt precipitates the albumin also. 



2. Heat Coagulation. — Saturate serum with magnesium sidphate and 

 filter off the precipitate ; preserve the filtrate and label it ' B.' Wash the 

 precipitate on the filter with saturated solution of magnesiiun sulphate imtil 

 the washings do not give the tests for albmnin,- then dissolve the precipitate 



' This may be conveniently done by a shaking machine before the class meets^ 

 ' On account of the prolonged nature of these opei-ations they must necessarily- 

 be performed by the demonstrator beforehand. ' 



