1. The milk and blood iodine of a herd of thirty Guernsey and thirty Holstein cows has been determined, previous to and during prolonged increased iodine feeding to one-half of the herd. The increased amount of iodine was fed as potassium iodide which was mixed uniformly with a grain feed.

2. The blood iodine of the iodized cows was greatly and uniformly increased.

3. The milk iodine was increased. This increase was principally dependent on the amount of iodine which was fed. During late spring, however, the milk iodine from both the iodized and control cows was unusually low. During early autumn the milk iodine from the iodized cows was low.

4. The milk from the iodized cows contained 7–26 times as much iodine as that from the control cows. An average milk iodine of 80μg. % was obtained from the iodized cows throughout a mid-year period of 5 months.

5. This experiment reveals that a milk of increased iodine content can be readily produced by increased iodine feeding.

The methods used for isolation and purification of bacteriophages active against lactic streptococci are described. An account is given of the relationships between nine apparently distinct phage races and eleven strains of lactic streptococci. The phages show a tendency towards strain specificity but there are some races which attack up to four different strains. Resistant strains usually arise on continued incubation of lysed cultures. Cross-resistance tests, in those cases where two or more phages act on one strain of streptococci, indicate that the relationships between the phages do not follow any simple rule.

1. Seventy-five pure cultures of various types of coliform bacteria were grown in sterilized or partially sterilized milk for 24 hr. at 17° C. The cultures of B. aerogenes, B. oxytocus and B. cloacae types as a rule multiplied much more rapidly than those of the B. coli types. Similar results were obtained when twenty-nine cultures of various coliform types were grown in raw milk for 24 hr. at 17° C. There was generally little or no tendency to clumping of the organisms in the milk, even after 3 days' incubation at 17° C.

2. Forty mixed cultures, each consisting of an aerogenes-cloacae type and a B. coli, were grown in milk for 24 hr. at 17° C. In thirty-four instances the aerogenes-cloacae type multiplied more rapidly than the B. coli.

3. Twenty-one of these mixed cultures were also grown in milk for 24 hr. at 22, 30 and 37° C. At 22, as at 17° C, the aerogenes-cloacae type multiplied as a rule more rapidly than the B. coli, while at 30 and 37°C. the reverse was the case.

4. Twelve specimens of bovine faeces were inoculated into raw milk and the cultures kept at 17° C. for 36 hr. Aerogenes-cloacae types occurring in the faeces became enriched in the milk, the coliform flora of the milk at the end of the incubation period frequently consisting chiefly of these types.

5. The greater incidence of aerogenes-cloacae types in summer milk in Scotland as compared with winter milk, found in a previous investigation, may be explained by the fact that when milk is contaminated directly or indirectly with faeces, these types become enriched at the temperatures of holding commonly employed in summer. Such enrichment does not occur in winter, the holding temperature of the milk being as a rule so low that there is little or no proliferation of any coliform types. Consequently, the relative proportions of the various coliform types in winter milk tend to remain similar to those in the faeces.

Of the lactic acid bacteria isolated, 720 strains from thirty-six typical Cheddar cheeses have been classified. The dominant organism in New Zealand cheese has been shown to be Sbm. plantarum. Sbm. casei occurs much less frequently, while betabacteria and betacocci are found in still smaller numbers. Betabacteria tend to replace Sbm. plantarum in the final stage of cheeseripening. The flora of good quality cheese has been found to consist mainly of one or two varieties of Sbm. plantarum, often associated with Sbm. casei or a small proportion of betabacteria. In poor-quality cheese a larger number of types of lactic acid bacteria frequently occur. A simple routine method is described for distinguishing the different groups present in cheese.

The effects which different strains of lactobacilli and betacocci produce in cheese have been correlated with their biochemical characteristics. Sbm. casei in general appears to be beneficial to cheese quality. The strains of Sbm. plantarum isolated have been grouped in four varieties, mainly on the basis of sugar reactions; one variety has been shown to be beneficial to cheese quality, another variety has very little apparent effect, while the remaining two varieties produce serious defects—bad flavours, discoloration and, occasionally, open texture. The same defects are produced by most strains of betabacteria and betacocci when present in large numbers.

The biochemical characteristics of the lactobacilli studied have shown a more regular gradation from Sbm. casei through Sbm. plantarum to Bbm. breve (the only species of Betabacterium isolated) than is indicated from the generally accepted systems of classification.

Attempts to improve the flavour of cheese by inoculation of good quality cheese-milk (pasteurized) with selected strains of streptobacteria gave the best results when relatively small inocula were employed. Large inocula imparted a sharpness to the flavour of the cheese during the early stages of ripening, and this sharpness often persisted when the cheese was mature.

Several possible methods suitable for the propagation of lactobacilli under factory conditions were investigated. The most convenient procedure consisted in the incorporation in the starter “mother” culture (enriched with a vegetable extract) of suitable strains of Sbm. plantarum; these strains were found to grow better in association with some starters than with others.

The pH ranges of growth of streptococci and lactobacilli in dextrose yeast casein digest broth have been studied. Nearly all the group I and II streptococci grew at pH 8·8, but only the enterococci grew at pH 4·8; all group III types (heterofermentative) grew at pH 4·4. Only a few lactobacilli grew at pH. 8·8 but most were able to grow at pH 4 if other conditions were favourable. The enterococci, Str. lactis and Str. cremoris could be differentiated by the alkaline limits of growth.

Indications of variability within pure strains of Str. cremoris have been studied.

In one strain changes in acid-producing power were made evident by changes in colony form. A variant which failed to ferment lactose but was still susceptible to the specific race of bacteriophage and exhibited the same morphology (after treatment at 37° C.) as the parent culture is described.

It was found that variation was well marked within some strains, especially in regard to acid production (or vitality), response to high temperature conditions, power to produce ropiness in milk, and degree of resistance to phage attack.

The destruction of vitamin C in milk under the action of light was studied in different containers. Brown glass bottles showed little destruction, green glass bottles considerably more, and wax impregnated cartons still more. Nevertheless, in the latter, twice as much vitamin C survived as in clear glass bottles.

1. By the use of sodium hexametaphosphate it is possible to eliminate the final filtration in the phosphatase test, and thus appreciably to shorten the time required for the test.

2. It is necessary to avoid direct sunlight during that part of the test in which Folin's reagent is in use. Other minor precautions are mentioned in the paper.

3. The pH. of the milk samples tested was found to vary naturally before pasteurization from pH 6·5 to 6·9 without affecting the validity of the test.

4. The test is also unaffected by the presence in milk of bacteria which produce reducing substances or which hydrolyse the substrate (sodium phenyl phosphate) unless the organisms are present in very large numbers.

By adapting Scharer's “10min. field test” to British conditions of pasteurization, an accurate phosphatase test has been evolved requiring less than 1½ hr. for completion. The method is described in detail.

A small percentage of anomalies was detected when applying the new method to the examination of pasteurized samples bulked from small quantities of milk (less than 100 gallons). This led to a study of several factors thought to be the likely cause of such anomalous results.

No correlation was found between the phosphatase surviving heat treatment and the stage of lactation when milk from individual cows and from small groups of animals was tested, with the possible exception of the early stages of lactation when the enzyme concentration before and after heating was frequently found to be low.

It was observed that pasteurized milk from animals suffering from mastitis tends to give abnormally high results of the phosphatase test. The amount of residual phosphatase is subject to considerable fluctuation.

1. The effects of alterations in the duration and speed of stirring on the apparent solubility of milk powders have been investigated. It is concluded that 30 sec. shaking of the powder reconstituted in a 10 % mixture is sufficient to dissolve the truly soluble portion of the dried milk, but that the protein which has become denatured during the drying process tends to pass into solution with increasing speed and duration of stirring.

2. A rapid method for estimating the solubility of milk powders on a total solids basis involving only 1 min. shaking is described and discussed.

3. The sediment method frequently used in industry as a guide to the solubility of dried milks is compared with the rapid method described in the present paper. At higher solubilities the sediment volume may serve as a guide to small changes in solubility, but in the lower solubility ranges its usefulness is very limited. It is shown that the washing of the sediment with one or more changes of water merely introduces additional errors into this method of solubility determination.