562 ACTION. OF CASEIN UPON SUGAR. 



Others, and exceedingly interesting to the practical agriculturist. Let 

 me explain this property a little more in detail. 



§ 15. Of the relations of casein to the sugars and the fats. 



1°. Relation to the sugars.— a. Production of lactic acid. — I have 

 already adverted (p. 543) to the remarkable property which casein pos- 

 sesses of gradually converting milk or other sugars into lactic acid. If 

 a small quantity c^ this substance, either in the state of fresh curd or in 

 the purer form juSt iescriijed, be introduced into a solution of cane-sugar, 

 or of sugar of milk, lactic acid begins very soon to be formed. Thus 

 the casein it contains is the cause of the souring of milk. In like man- 

 ner it is the casein contained in bean or pea-meal v^^hich makes it so 

 soon become sour when mixed with water. 



h. Production of butyric acid. — But the transforming action of casein 

 doos not end when this change is produced. After a longer time a 

 further alteration is ^ected by its means. A fermentation commences, 

 during wdiich carbonic acid and pure hydrogen gases are given off, and 

 butyric acid is produced (Pelouze and Gelis). Let us consider the 

 nature of this new^ change. 



Butyric acid is represented by Cs Hs O4 ; and lactic acid, as we have 

 seen, by Ce He Oe ; therefore — 



4 of lactic acid = C24 H24 O24 and 



3 of butyric acid = C24 H24 O12 



Difference O12 



That is to say, that 4 of lactic acid, in order to be converted into 3 of 

 butyric acid, must give off 12 of oxygen. But 'during the fermentation 

 which accompanies the change no oxygen is given off. The gases 

 which escape are carbonic acid and hydrogen. The oxygen given off 

 by one portion of the lactic acid, therefore, must combine with the ele- 

 ments of another portion, and convert it into these gases. Thus to — 

 1| of lactic acid . . = C9 H9 O9 

 Add 12 of oxygen . . = O12 



9 of carbo- , 6 of liy- , 3 of 

 nic acid "*" drogen "* water. 



And we have . . . Cg H9 O21 = 9 C O2 + 6H -f 3 HO ; 

 or, while 4 atoms of lactic acid are converted into 3 of butyric acid, 1^ 

 of lactic acid are at the same time converted into 9 of carbonic acid gas, 

 6 of hydrogen gas, and 3 of water. The gases escape and cause the fer- 

 mentation, while the water remains in the solution.* 



* I have taken in the text the smallest numbers by which the general change could be re- 

 presented in the simplest way. According to Pelouze and Gelis, however, the hydrogen 

 given off is sensibly one-third of the bulk of the carbonic acid when the butyric fermenta- 

 tion is in its vigour. To satisfy this condition, therefore, much higher numbers must be 

 taken ; such as the following: — 



20 of lactic acid = Cf^o H|'A O120 are converted into 



15 of butyric acid = Cl'^^o Hiio Oeo 



Giving off = Oeo 



And these CO of oxygen decompose 6 of lactic acid, as above described. Thus to — 



6 of lactic C36 H;j6 (m 



Add 60 of oxygen . . Ogo 



6 of carbonic acid -1- 12 hydrogen + 24 water. 



And we have . . C36 H36 09C z= 36COJ + ]2Ii + 24HO, 



where the carbonic acid gas i? exactly three times the bulk of the Hydrogen gaj produced. 



