REACTIONS OF CASEOSES. 59 



The curd produced by rennet contains for 0-477 per cent, of 

 casein nitrogen : 



Nitrogen, 0-416 



CaO, 0-119 



P 2 5 , 0-117 



Ash, .0-23 



and the quantity of caseose nitrogen left in the whey is 



0-061 



The acidity of the whey was found to be 8-4 c.c. of normal 

 alkali per litre less than that of the milk. 



These figures are in accordance with the view that casein in 

 milk is split by rennet into two compounds containing 116 and 

 18 atoms of nitrogen respectively, the former containing all the 

 sulphur and phosphorus of the casein. 



The whey caseose is free from tyrosine and tryptophane, 

 When acted on by lactic acid the curd protein forms lactates. 

 which have the property of becoming stringy when heated. 



If calcium be removed from milk the action of rennet differs, 

 and a whole series of caseoses is formed, and no curd is produced. 

 Casein and its immediate derivatives appear to have the power 

 of forming with tricalcium phosphate very insoluble salts. 



Reactions of the Caseoses. 



Dys-caseoses. These products in the pure state are soluble 

 in water ; they combine with calcium salts, especially phos- 

 phates, to form insoluble compounds. 



The following reactions are given by dys-pepto -caseose ; the 

 other dys-caseoses behave similarly. 



Acetic acid in moderate excess gives an insoluble white pre- 

 cipitate, soluble in large excess on heating. 



Hydrochloric and sulphuric acid give precipitates, also soluble 

 in large excess on heating. Even 0-2 per cent, hydrochloric acid 

 produces complete precipitation. 



Nitric acid gives a precipitate far more easily soluble in excess 

 of acid. On warming, the solution turns yellow, and, with 

 ammonia, gives the orange-yellow colour of the xantho-protein 

 reaction. 



With a little copper sulphate and an excess of caustic potash 

 the violet colour of the biuret reaction is given. 



Cupric sulphate and ferric chloride precipitate dys-caseose. 



Ammonium sulphate added to saturation precipitates dys- 

 caseose, but sodium chloride does not. Addition of acetic acid, 

 however, to the salt-saturated fluid gives the usual precipitate of 

 dys-caseose. 



