that methods of milk analysis formerly used tended to underestimate the fat and overestimate the other solids.

The Commission on Milk Standards appointed with a view to securing uniformity of requirement among the different states and cities of the United States has recommended the general adoption of the standard calling for not less than 3.25 per cent of milk fat and not less than 8.5 per cent of milk solids-notfat, as previously proposed by the Association of Official Agricultural Chemists.

The Commission also recommended the adoption by communities of regulations providing for the sale of milk on a basis of guaranteed composition. The advantage of such a system is apparent from the fact that any single legal minimum must necessarily be set considerably below the average in order to provide for natural variations in composition. Average milk and milk considerably below the average are thus equally legal, though of different value. It would obviously be fairer both to producer and to consumer if all milk could be sold on the basis of its true value.

In addition to standards of chemical composition several communities have adopted sanitary or bacteriological standards. Thus milk which contains visible dirt or more than a certain number of bacteria may be forbidden sale, or (as in the case of New York City) a maximum temperature may be prescribed on the ground that in warm milk bacteria multiply so rapidly as to make it a "decomposed substance" if not an actual menace to health. Until recent years such sanitary and bacteriological standards as existed varied much with the locality and were generally regarded as more or less tentative; but such standards are now becoming stabilized and are playing an important part in the steady improvement of the sanitary quality of the milk supply. The reader can doubtless ascertain the current standards of his own locality by inquiring of the city health department or the state food commissioner.

Classification Recommended by Commission on Milk Standards

GRADE A

Raw milk. Milk of this class shall come from cows free from disease as determined by tuberculin tests and physical examinations by a qualified veterinarian, and shall be produced and handled by employees free from disease as determined by medical inspection of a qualified physician, under sanitary conditions such that the bacteria count shall not exceed 100,000 per cubic centimeter at the time of delivery to the consumer. It is recommended that dairies from which this supply is obtained shall score at least 80 on the United States Bureau of Animal Industry score card.

Pasteurized milk. Milk of this class shall come from cows free from disease as determined by physical examinations by a qualified veterinarian and shall be produced and handled under sanitary conditions such that the bacteria count at no time exceeds 200,000 per cubic centimeter. All milk of this class shall be pasteurized under official supervision, and the bacteria count shall not exceed 10,000 per cubic centimeter at the time of delivery to the consumer. It is recommended that dairies from which this supply is obtained should score 65 on the United States Bureau of Animal Industry score card.

(Note. The above represents only the minimum standards under which milk may be classified in grade A. The commission recognizes, however, that there are grades of milk which are produced under unusually good conditions, in especially sanitary dairies, many of which are operated under the supervision of medical associations. Such milks clearly stand at the head of this grade.)

GRADE B

Milk of this class shall come from cows free from disease as determined by physical examinations, of which one each year shall be by a qualified veterinarian, and shall be produced and handled under sanitary conditions such that the bacteria count at no time exceeds 1,000,000 per cubic centimeter. All milk of this class shall be pasteurized under official supervision, and the bacteria count shall not exceed 50,000 per cubic centimeter when delivered to the consumer.

It is recommended that dairies producing grade B milk should be scored and that the health departments or the controlling departments, whatever they may be, strive to bring these scores up as rapidly as possible.

GRADE C

Milk of this class shall come from cows free from disease as determined by physical examinations and shall include all milk that is produced under

conditions such that the bacteria count is in excess of 1,000,000 per cubic centimeter.

All milk of this class shall be pasteurized, or heated to a higher temperature, and shall contain less than 50,000 bacteria per cubic centimeter when delivered to the customer. It is recommended that this milk be used for cooking or manufacturing purposes only.

Whenever any large city or community finds it necessary, on account of the length of haul or other peculiar conditions, to allow the sale of grade C milk, its sale shall be surrounded by safeguards such as to insure the restriction of its use to cooking and manufacturing purposes.

The above recommendations have been indorsed by the American Public Health Association, the American Medical Association, and the Conference of State and Provincial Boards of Health of North America. They have formed the basis for the regulations of many cities, though modifications of detail are naturally often introduced to meet local conditions.

Detailed Composition

The proteins of milk. From three fourths to four fifths of the nitrogenous matter of cows' milk consists of caseinogen (casein, calcium-casein), while most of the remainder is in the form of lactalbumin; other proteins have been found in very small amounts, among these lactoglobulin has long been known and an alcohol-soluble protein has recently been described by Osborne and Wakeman, who suggest that milk may also contain extremely small quantities of proteoses.

Caseinogen or casein is the best known of the phosphoproteins. Lactalbumin contains no phosphorus but is richer in sulphur than is casein. The elementary composition of these two proteins is shown in Table 4, while in Table 5 are given the amounts of the different amino acids obtained from the hydrolysis of each.

By comparison with the corresponding data given in later chapters it will be seen that the yields of several of the more complex amino acids such as tryptophane, tyrosine, and lysine

are distinctly higher from the milk proteins than from food proteins in general; while the amino acids lacking or present only in small quantity in milk proteins are, in most cases, those of which the body may readily derive abundant supplies from other sources. (See also the sections on nutritive value and place in the diet in this and succeeding chapters.)

TABLE 4. ELEMENTARY COMPOSITION OF CASEIN AND LACTALBUMIN

1 In general the highest yield of each amino acid is given since it is known that the methods used tend to give results below the truth.

To separate all the amino acids which a protein yields and determine the amount of each one as shown in Table 5 requires a large quantity of purified material and the devotion of an enormous amount of time to most difficult and intricate research methods. With much smaller quantities of purified material and a more moderate expenditure of time and labor a partial knowledge of the "amino-acid make-up " of a protein may be obtained by the method of examination devised by Dr. D. D. Van Slyke. This Van Slyke method determines how the total nitrogen of the protein is divided among eight fractions or forms of combination, four of which are individual amino acids of much importance in nutrition and therefore very significant in our judgment of food values. The results of such an examination of casein and lactalbumin are shown in Table 6.

TABLE 6. DISTRIBUTION OF THE NITROGEN OF MILK PROTEINS AMONG THE FORMS DETERMINABLE BY THE VAN SLYKE METHOD (EXPRESSED AS PERCENTAGE OF THE TOTAL NITROGEN OF THE PROTEIN)

It is to be remembered that data of the two kinds illustrated by Tables 5 and 6 cannot be compared directly because expressed on different bases: in the one case as weight of amino acid obtained from one hundred parts by weight of protein, in the other as the percentage of the total nitrogen which is found to exist in a particular form. Also the nature of the methods is such that data such as those in Table 6 regularly show a summa