156 Bulletin of Laboratories of Denison University voi.xi.j 
why should there b'e this difference between his culture and nor- 
mal cheese ? And when we seek an explanation of the curing 
process, the case is not at all clear. The ripening consisted in 
the conversion of the insoluble casein into soluble peptones or 
allied products. That the acid is not produced by the activity 
of the germ upon the casein, can scarcely be questioned. Its 
only source is in the milk sugar. Is the acid produced, then, 
to react upon the casein and break it down ? No such action 
is known to chemists, but what are the facts ? To test this 
question a special experiment was devised. Lactic acid was 
added to curd made from pasteurized milk, and the same was 
made into cheese. No evidence could be obtained that the acid 
produced the change in question. Can there be a difference in 
action between commercial lactic acid and that produced in the 
cheese, especially in the nascent state ? 
The problem was then attacked in another way. If the 
acid production in the cheese could be inhibited, would the pro- 
cess of curing also be inhibited ? To test this ether, chloro- 
form, etc., were added to newly made cheese and the same 
were kept in an atmosphere saturated with these anaesthetics. 
These cheese cured, apparently, quite normally. Bacteriolog- 
ical analyses revealed bacteria, but in greatly reduced numbers — 
too small to account for the curing. That bacteria were pres- 
ent is readily explained, for they were not killed by the anaes- 
thetics but their vital activities were inhibited. But the break- 
ing down of the casein and curing of the cheese still remains to 
be explained. If the bacteria are inhibited in their vital activi- 
ties, then no acid can have been produced to affect the casein. 
But the casein underwent its characteristic change. Plainly 
there is an unknown factor which is the cause of this phenome- 
non. That factor is not related to bacterial life. 
It was at this stage of the problem that Drs. Babcock and 
RusseP sought to apply chemical ‘tests to determine the 
unknown factor. It is here that their brilliant work in isolat- 
* Babcock and Russell, Unorganized ferments of milk: a new factor in the 
ripening of cheese. 14th Kept. Wis. Agrl. Stat. 1897, p. 161. 
