38 INTRODUCTORY — THE COXSTITUEXTS OF MILK. 



not, however, precipitated by acids, and are less readily preci- 

 pitated by copper sulphate. 



Laeto - Globulin. — This protein is coagulated by heat and 

 precipitated by neutral sulphates, tannin, etc. ; rennet does not 

 coagulate it. It coagulates at 72° C. It only occurs in traces 

 in milk, but in larger amounts in colostrum. It is not known 

 whether it difiers chemically from serum-globulin. Its chief 

 characteristic is its solubility in sodium chloride solutions even 

 when acidified. 



Storch's Mucoid Protein.— The foUov.-ing properties are 

 given by Storch : — Washed with alcohol and afterwards with 

 ether, and dried in air at the ordinary temperature, it forms 

 a loose, fine, hygroscopic powder of a greyish-white colour. It 

 is insoluble in dilute ammonia and acetic or h-ydrochloric acids ; 

 it swells considerably without dissolving in weak solutions of 

 alkalies, and is only partly soluble in dilute potassium or sodium 

 hydroxide. It gives the reactions of proteins — i.e., red color- 

 ation with Millon's reagent, brown colour with iodine and yellow 

 with nitric acid and ammonia (xantho-protein reaction). A\'hen 

 heated with dilute hydrochloric acid it yields a substance which 

 reduces Fehling's solution ; the amount of copper reduced is 

 6 '5 parts for each 100 parts of dr)- ash-free substance. It gives 

 also the biuret reaction. 



It contains 14-76 per cent, of nitrogen and 2-2 per cent, of 

 sulphur, of which only a small portion is lemoved by boiling 

 with alkalies. 



Preparation of Mucoid Protein. — (i.) The author has found 

 the easiest method is to centrifuge sweet butter milk and 

 wash the deposit several times with water made faintly alkaline 

 with ammonia, the deposit being separated each time by centri- 

 fugal action. The mass is treated with strong alcohol, and after- 

 wards with ether, and dried in vacuo. 



(ii.) Storch has prepared it from butter, by melting 1 to 2 lbs. 

 at a low temperature; the fat is carefully "decanted ; and the 

 liquid rinsed twice with benzene, diluted with distilled wntev 

 and mixed with one and a half times its volume of strong alcohol. 

 The precipitate is washed with 60 per cent, alcohol and extracted 

 with ether till all fat is removed, and air dried. 



(iii.) Fresh cream (about 30 per cent, fat) is diluted with four 

 times its volume of a 33 per cent, solution of cane sugar and 

 placed in a large separating funnel ; after a dav's repose, the 

 sugar solution is drawn off, and the remaining cream again 

 mixed with four times its volume of the sugar solution : "this 

 process is repeated four times and the washed cream is shaken 

 with an equal volume of strong alcohol, and twice as much ether 

 .and some benzene are added. A gelatinous precipitate separates 



