202 -TWENTY-FIFTH ANNIVERSARY REPORT: 
Station and has been continued since at intervals. The results have 
been published in the following Bulletins: No. 214 (A study of the 
salts formed by casein and paracasein with acids; their relations 
to American cheddar cheese); No. 245 (Chemical changes in the 
souring of milk); No. 261 (Some of the relations of casein and 
paracasein to bases and acids and their ‘application to’ cheddar 
cheese) ; Technical Bul. No. 3 (The action of dilute acids es 
casein when no soluble compounds are formed). 
In connection with a‘study of the chemical changes that occur 
in cheese-ripening, it was observed that in the operation of cheese- 
making a substance is formed which is soluble in a warm (55° C.) 
5 per ct. solution of sodium chloride and also in hot 50 per ct. 
alcohol. This substance appeared to be formed only when an acid 
was present ‘in certain amount.. When this salt-soluble substance 
was treated with more acid, it was changed into a substance 1mn- 
soluble in dilute salt solution: It was also: found that, when milk 
is treated with a certain amount of acid, a coagulum is formed 
soluble in salt solution and that, when more acid is added, the ‘salt- 
soluble substance is changed into one not soluble in dilute salt solu- 
tion. This action was explained by saying that when milk-casein or 
paracasein is treated with an acid, it unites with the acid in a certain 
proportion, forming a casein salt of the acid which is soluble in 
warm dilute salt solution; and that this compound, when treated 
with more acid, unites with twice as much acid as the first com- 
pound, forming a substance which is not soluble in warm, dilute 
salt solution. The salt-soluble substance was called casein (or para- 
casein) monolactate and the second substance casein (or paracasein) 
dilactate. -It was later. found that the above explanation, owing 
to imperfect experimental work, was erroneous. It was then sup- 
posed, as the result of further work, that the: salt-soluble substance 
-(monolactate) was simply base-free casein (or paracasein), con- 
‘taining no acid:at all in-combination, in other words, milk-casein 
‘(calcium casein) from which the calcium had been removed by the 
acid, forming a calcium salt of the acid and calcium — free casein. 
It-was then believed that the insoluble substance resulting from treat- 
ment with further acid (dilactate) was a simple, definite combina- 
tion of casein (or paracasein), one gram of casein (or paracasein) 
combining: with an amount of acid equivalent to about.0.5° cc. of 4 
hydrochloric acid. This conclusion was based on the fact that when 
casein is shaken with acid and filtered, some of the ‘acid is:taken 
up by the casein from the solution. In reviewing this work later, 
