ALKALI-FORMING BACTERIA FOUND IN MILK. 
27 
In order to show whether the alkaline reaction was due to the 
production of carbonates or bicarbonates, or both, Table 12 has been 
prepared, using the organic acids which were utilized as test sub- 
stances in this investigation. Here again attention is called to the 
fact that the essential process in the production of an alkaline reaction 
is the replacement of the relatively strong organic acids by the 
relatively weak carbonic acid. The figures in the table are based 
on the complete oxidation to the carbonate or bicarbonate of 100 c. c. 
of a 0.1 per cent solution of the acid. In the next to the last column 
of the table the tenth-normal equivalent is given in cubic centimeters 
for both the carbonate and bicarbonate. This table should be 
studied in connection with the plot in figure 1 which represents the 
change of any of the 
test acid salt media 
from the initial P H 6.9. 
The resulting hydro- 
gen-ion concentration 
obtained when known 
amounts of tenth-nor- 
mal NaHCOg were 
added to the medium 
above is represented 
by one curve. The 
other curve was ob- 
tained similarly by 
plotting the resulting 
hydrogen-ion concen- 
tration when known 
amounts of tenth-nor- 
mal JN a 2 C O 3 Were fig. I.— Curve showing effect of addition of bicarbonate and sodium 
added to the Same carbonate on the reaction of the sodium-ammonium-phosphate 
. ,. T medium. 
synthetic medium. It 
will be noted that the large quantity of alkali generated by some 
of the fermentations could not possibly be due to the complete 
oxidation of the acid to bicarbonate. Let us take, for example, 
propionic acid; on complete oxidation this acid yields an equivalent 
of 1.3 cubic centimeters of tenth-normal alkali. From the curve it 
is seen that 1.3 cubic centimeters of tenth-normal alkali gives a hy- 
drogen-ion concentration of P H 7.9 while the average hydrogen-ion 
concentration of the alkali group of bacteria which fermented pro- 
pionic acid was P H 7.4. 
From this it is evident that the entire amount of alkali produced 
from this organic-acid salt might be accounted for by the production 
of sodium bicarbonate. On the contrary, if we examine the figures for 
glyceric acid it will be found that this acid on complete oxidation yields 
an equivalent of 0.94 cubic centimeters tenth-normal alkali 7 which corre- 
*># 
A/aftCQ 
_ |\ A/agCOj 
/.o /.s 
Cub/c centimeters of 
