
MILK PRESERVED AT SEVENTY AND FIFTY DEGREES. 47 _ 
2. Comparison of the number of acid bacteria in fresh milk 
with the number tn milk 50 hours old.—A study of column 6 in 
Tables 3 and 4 shows that the acid bacteria increased very 
greatly in relative proportion. during 50 hours at 70°. In 
nearly every case milk which was 50 hours old contained bac- 
teria of which 99 per cent. of the total number were acid 
bacteria. Usually these bacteria consisted of Bac. lact?s acidi 
in large percentage, even though this species was found only in 
small numbers in the fresh milk. Such a large proportion of 
acid bacteria, of course, left the percentage of non-acid organ- 
isms at 50 hours very small. In a few samples the presence 
of acid producing organisms at 50 hours seems to be somewhat 
less in the strained samples than in those which were not 
strained, but the difference is too slight to have any signifi- 
cance. It will also be noticed that in the samples where the 
acid organisms were few the number of liquefying bacteria was 
rather high. From this the conclusion is reached that strain- 
ing the milk has no influence whatsoever upon either the total 
number or the percentage of acid bacteria that may be expected 
in the milk after it has been kept for 50 hours at 70°. 
3. Development of acid.—In column g is shown the amount 
of acid which was present in the milk at 50 hours. It will be 
seen from this.column, first, that even in cases where the acid 
bacteria at 50 hours had reached 99 per cent., the amount of 
acid present in the milk was not increased very greatly. The 
highest per cent. of acid was obtained on Dec. 31,* when there 
was .63 per cent. at 50 hours. In other cases the percentage of 
acid was comparatively small; for example, on Jan. 16 and 18 
the amount of acid was only .26 per cent. at 50 hours, even 
though the milk contained at the time 199,000,000 and 282,- 
750,000 bacteria per cubic centimeter respectively, of which 
lactic bacteria constituted 99 per cent. of the whole. This fact 
suggests that the production of acid takes place rapidly only after. 
the acid organisms have gained full control of the milk. Fur- 
ther examination of column 9 in Tables 3 and 4 shows that the 
effect of straining is practically nothing. It is true the average 
per cent. of acid in Table 3 is slightly greater than in Table 4, 
_38 per cent. against .35 per cent., but this difference is so slight 
as to have no meaning; and when the individual experiments 
in the two tables are compared with one another, it is seen that 
* Table 3. 
