46 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
terms are very indefinite and have been frequently used 
indiscriminately. Since 1893, milk produced under the 
supervision of a medical milk commission has been sold 
under the name of certified milk, but the term has also 
been applied to milk which was not produced under these 
conditions. The desirability of defining the special 
names used for milk, and the advantage to both the pro- 
ducer and consumer of grading or classifying market 
milk according to its hygienic quality, has long been 
recognized, but no definite steps were taken in the matter 
until 1907 when Melvin’ proposed that market milk 
be graded in three classes, as follows: 
Class 1. Certified Milk.—This may be briefly defined as milk 
produced in accordance with the requirements of the American 
Association of Medica] Milk Commissions (see Appendix). 
Class 2. Inspected Milk.—This term should be limited to 
clean raw milk from healthy cows, as determined by the tuber- 
culin test and physical examination by a qualified veterinarian. 
The cows are to be fed, watered, housed, and milked under good 
conditions, but not necessarily equal to the conditions provided 
for Class 1. All persons who come in contact with the milk 
must exercise scrupulous cleanliness, and must not harbor the 
germs of typhoid fever, tuberculosis, diphtheria, and other in- 
fections liable to be conveyed by the milk. This milk is to be 
delivered in sterilized containers, and is to be kept at a tempera- 
ture not exceeding 50° F. until it reaches the consumer. It shall 
contain not more than 100,000 bacteria per cubic centimetre. 
Class 3. Pasteurized Milk.—Miulk from the dairies not able 
to comply with the requirements specified for Classes 1 and 2 
is to be pasteurized before being sold, and must be sold under 
the designation “ pasteurized milk.” Milk for pasteurization 
shall be kept at all times at a temperature not exceeding 60° F. 
while in transit from the dairy farm to the pasteurization plant, 
124th Annual Report, U. S. Bureau of Animal Industry, 
pp. 179 to 182. 
