PROTEINS OF MILK. 49 



Bechamp supposes that the proteins of milk number three 

 casein, albumin, and a body having the properties of an 

 enzyme, which he calls galacto-zymase ; this enzyme he finds 

 liquefies starch paste, evidently not its normal function in milk ; 

 his results have not been confirmed. He also supposes the 

 casein and albumin to exist in milk in combination with bases 

 (soda, lime, or potash). 



Biel has described syntonin as a normal constituent of milk, 

 but the existence of this must be considered doubtful at present. 



Palm has stated that albumoses are found in milk ; this is 

 probably not wholly correct ; it is possible that traces of albu- 

 moses are formed during the decomposition to which milk is 

 prone, but no other observer has identified more than traces, 

 while Palm gives 1-5 per cent, as occurring in milk. True 

 peptone has been proved to be absent. Storch's researches 

 have been referred to (p. 2). Babcock has found very small 

 amounts of nuclein, but the presence of this has now been 

 disproved. When it is considered, however, that proteins are 

 formed by the condensation of a large number of amino-acids, 

 and, therefore, a large number of isomers must be possible, 

 it would not be surprising if what we know as proteins are not 

 really mixtures of isomeric bodies. 



From the above list of the various proteins described as existing 

 in milk we may select the five of whose existence we have the 

 strongest evidence ; these are casein, lactalbumin, lacto-globulin, 

 Storch's mucoid, and the alcohol soluble casein ; the last three, 

 however, are only found in traces in milk, and, practically, the 

 proteins may be reduced to the former two. The other compounds 

 described, except the enzymes whose proteinic nature is not fully 

 established, are hypothetical. 



The main reactions that distinguish the five proteins of milk 

 are as follows : Casein is precipitated by saturating the solution 

 with sodium chloride, magnesium sulphate, and ammonium 

 sulphate ; globulin is soluble in a saturated solution of sodium 

 chloride, but is precipitated by magnesium and ammonium 

 sulphates ; albumin is soluble in saturated solutions of sodium 

 chloride and magnesium sulphate, but is precipitated by satura- 

 tion with ammonium sulphate, while Storch's mucoid is not in 

 solution, and the fifth protein is soluble in alcohol, but other- 

 wise has all the properties of casein ; albumin is, however, 

 precipitated from a saturated solution of magnesium sulphate 

 by acidifying slightly, and is redissolved by neutralisation of 

 the solution. Casein and globulin are precipitated by the addi- 

 tion of acid, while albumin (and globulin, if much salt is present) 

 is not so precipitated. Casein has the remarkable property of 

 being acted on by chymase, the enzyme of rennet, with the 



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