30 REPORT OF THE BACTERIOLOGIST OF THD 
INTRODUCTORY.—FLAVOR IN MILK AND ITS PRODUCTS. 
In milk, and more especially in butter and cheese produced 
from it, flavor is the quality most noticed by the consumer. in 
milk the volatile compounds which impress themselves upon our 
senses are ordinarily spoken of as odors, while in butter and 
cheese they are usually included under flavor; although in the 
case of the expert, at least, they are determined in both cases by 
the sense of smell. In this discussion of flavor we will not at- 
tempt to distinguish between the impressions received through 
the ordinary act of smelling, as practised by the cheese judge, 
and the sensations received by tasting, in the case of the con- 
sumer. To be sure, in the latter act the sensations of acidity, 
bitterness and sweetness derived from the tongue are added. to 
those received from the volatile compounds floating up to the 
olfactory membrane above. 
SENSH OF SMELL NOT AN BXACT STANDARD. 
Because the amount of this volatile matter is so slight we are 
without any exact standard of measurement, and in an attempt 
at careful work upon the subject recourse has been had to the 
sense of smell of a trained individual in order to judge the results 
obtained. When the work has to do with a very pronounced 
flavor of any kind this method gives satisfactory results; but 
when the presence of faint and complex odors is involved, as is 
the case with ripening cheese, the opinions of equally skilled and 
impartial judges often differ considerably. 
In the past little work has been done upon this subject, except 
upon butter flavors, but there has grown up considerable infor- 
mation based upon isolated and more or less questionable obser- 
vation. | . 
TWO GENERAL CLASSES OF FLAVORS. 
On the basis of their origin these flavors may be divided into 
two general classes—one directly connected with the growth of 
plant life in the milk, the other due to compounds taken up while 
in the cow or absorbed after the milk is drawn. 
