BY A. H. MOSBLEY AND H. G. CHAPMAN. 577 



Iii considering the cause of this destruction, the results that 

 have been obtained in the presence of other sodium salts must 

 be remembered. Since sodium lactate had little or no action 

 upon clotting, it would appear that sodium hydrate did not 

 react with lactic acid and form sodium lactate. Again, since 

 sodium chloride and di-sodium hydrogen phosphate had likewise 

 no rapid deleterious action upon rennet, the sodium ion must be 

 excluded as the cause of the destruction of rennet. Since the 

 relative concentrations of sodium and calcium ions present did 

 not need to be altered to produce clotting (see Table xiii.) it 

 would appear that the increased mass of sodium was not respon- 

 sible for the failure of the formation of a clot. Destruction of 

 the rennet with no conversion of caseinogen into casein is, there- 

 fore, to be regarded as the principal factor in the prevention of 

 clotting by the soda. 



In the further elucidation of this question certain general 

 considerations are of value. Milk contains salts of phosphoric 

 acid, both in suspension and solution, and when fresh both 

 hydrogen and hydroxyl ions are present. Within certain limits 

 the addition of free acid or alkali will occasion little alteration 

 in the concentrations of hydrogen or hydroxy] ions. Instead 

 there will be a slow conversion of mono-hydrogen to di-hydrogen 

 phosphate or vice versa with the object of eliminating any excess 

 of hydrogen or hydroxyl ions. The addition of acid or alkali 

 to milk will thus not lead to a marked alteration in the acid or 

 alkaline nature of the fluid, but to an alteration in the type of 

 the phosphates present in the milk. 



When milk stands for some hours after milking, acid is produced 

 by the lactic acid bacilli in the milk. This lactic acid interacts 

 with the di-sodium phosphate and other mono-hydrogen phos- 

 phate in the milk forming as a result lactate and di-hydrogen 

 phosphate. 



HC 3 H 6 8 + Na 2 HP0 4 = NaC 3 H 5 3 +NaH 2 P0 4 



As is well known, the lactic acid bacilli do not multiply in 

 culture media unless means are adopted to neutralise the lactic 

 acid as it is formed. This neutrality is usually assured by the 



