ELEMENTARY PHYSIOLOGICAL CHEMISTRY 187 



EXPERIMENT IV. Take a pure solution of caseinogen. Divide it 

 into two portions a and b. To both add about ten drops of rennin 

 ferment. To b add also a few drops of a 5 per cent, solution of 

 calcium chloride. Place both in the water bath at 40 C.; after about 

 five minutes examine to see if clotting has occurred. It will be found 

 that clotting has occurred in b where both rennin and soluble Ca salts 

 were present. 



EXPERIMENT Y. Repeat the experiment with two samples of fresh 

 milk a and b. To b add, instead of CaCl 2 , some potassium oxalate 

 solution. In this case only a will clot. The potassium oxalate has 

 robbed the portion b of its soluble calcium salts. It can be made 

 to clot by adding calcium chloride solution. 



From these experiments we see, therefore, that the clotting of milk 

 depends on the transformation of a soluble proteid, caseinogen, into an 

 insoluble derivative, casein, by means of a ferment, rennin ; and, further, 

 that the presence of soluble calcium salts is necessary for this process. 



It is probable that there are two stages in this transformation : the 

 rennin first splits the caseinogen into two bodies, the more important 

 being soluble casein, which then combines with Ca salts to form 

 casemate of calcium or casein, while the other passes into solution in 

 the whey as whey-proteid (see Advanced Course, p. 436). 

 Caseinogen 



Whey-proteid Soluble casein + soluble Ca salts 



(goes into solution). = caseinate of calcium or casein. 



The casein thus produced entangles the emulsified fat globules of the 

 milk, and forms the curd of milk. This curd shrinks after a few hours, 

 and an opalescent fluid is squeezed out of it called whey. The whey 

 contains, besides whey-proteid, traces of other proteids and also the 

 carbohydrate (lactose) and salts of milk. 



EXPERIMENT VI. Apply the xanthoproteic reaction to some whey : 

 a positive result is obtained. Acidify some of the whey with acetic 

 acid and boil ; the proteid is coagulated. The proteids are called 

 lacto-albumin and lacto-globulin. 



II. The Carbohydrate is Lactose. 



EXPERIMENT VII. Boil some whey which has been weakly acidified 

 with acetic acid. Filter off the coagulated proteids. To the filtrate 

 apply Trommer's or Fehling's test ; reduction is effected. 



Lactose does not, like dextrose, readily ferment with yeast, but it is 



