180 REPORT OF THE CHEMISY OF THE 
4, Even in the cases where the largest amounts of lactic acid 
were used, the acid disappeared as free acid. This was shown 
by making a titration of the water-extract of the curd with +5 
sodium hydroxide, using phenol-phthalein as indicator. It is 
readily seen that the number of cc. of alkali required for neu- 
tralization represents a very small amount of acid, compared 
with that furnished in Series. A, B, D, E, and F. The acid 
had largely combined with paracasein to form products only 
slightly soluble in water. 
The question may be raised here as to what it is in the water- 
extract that neutralizes alkali. In Series C it is, in all proba 
bility, direct neutralization by proteid, as no acid was present. 
In Series F, on the other hand, there is probably some free 
acid, aS an excess of acid was used. In most cases, however, 
the neutralization is due, apparently, to a water-soluble com- 
pound of acid and proteid, as shown by the fact that only in 
cases where acid was furnished, whether by fermentation or by 
direct addition, a precipitate appeared on neutralization, and 
such a precipitate would be expected only in the case of a 
combination of acid with proteid. The larger the amount of 
alkali required by the water-extract for neutralization, the more 
abundant was the precipitate appearing on neutralization. 
Just here, the main point we desire to consider is an explana: 
tion of the fact to which attention has been called above, viz.: 
that from a given amount of paracasein treated with a certain 
amount of lactic acid, we obtain a maximum yield of our salt- 
soluble product; while an increase of acid beyond a given 
‘amount decreases the yield of salt-soluble product. We might 
naturally expect that increase of acid would yield an increase 
of salt-soluble product from a given quantity of paracasein. 
How can we explain this? The explanation that agrees most 
satisfactorily with the experimental data at hand in this: Para- 
casein combines with lactic acid in at least two different pro- 
portions, forming two distinct compounds. One of these com- 
pounds is the unsaturated salt and is soluble in dilute solutions 
of sodium chloride; it is this compound that is present in normal 
cheddar cheese. The other compound is the saturated salt 
