1. The influence of temperature, pH, oxygen tension and yeast autolysate on the production of by-products and the ratios of by-products formed to sugar utilized and lactic acid produced in milk by the heterofermentative lactic acid streptococci has been investigated.

2. The total production of lactic acid is increased by anaerobic conditions and low temperature. The ratio of lactic acid formed to sugar utilized is increased by anaerobic conditions and the presence of chalk.

3. The total amount of acetic acid is higher in the presence of chalk, at the lower temperatures and in yeast milk, but is decreased by anaerobic conditions. The ratio of acetic acid both to sugar utilized and to lactic acid formed is smaller at lower temperatures, in the presence of “growth factors” and chalk and under anaerobic conditions.

4. The total alcohol production is higher when yeast or chalk is added to milk, under anaerobic conditions and at lower temperatures, and similarly the ratio of alcohol formed to sugar utilized and lactic acid produced is increased.

5. Hydrolysis of residual lactose occurred in all cultures of Str. citrovorus and with some of the other streptococci in cultures to which chalk had been added.

6. Although the heterofermentative lactic acid streptococci possess respiratory enzymes, these fail to suppress aerobic fermentation (i.e. the Pasteur effect is slight).

The times needed for the complete inactivation of bacteriophages for the lactic streptococci by several chemical disinfectants in various strengths were determined. The phage preparations, consisting essentially of whey, contained the usual amounts of protein and lactose, so that the results obtained must be considered applicable only under the defined conditions. Hydrogen and hydroxyl ions were found to inactivate phage when they were present in sufficient concentration but their effects between pH. values of 4 and 7 were negligible over several days at room temperature.

By far the most effective of the disinfectants were active chlorine and permanganate, which suggests that the inactivation of phage is most readily brought about by oxidation.

In the milk of herds “free” from streptococcus infection, the presence of staphylococci has been shown to accompany chemical changes in the composition and abnormalities of pH.

In mastitis control schemes, based on Str. agalactiae infection, cases of staphylococcus infection are missed because of suppression of growth on the routine crystal violet blood agar of Edwards. Further, as clinical cases of staphylococcus mastitis causing serious disturbance are comparatively rare, the subclinical type may be present to a considerable extent and yet remain unsuspected. Thus in herds free from streptococcus mastitis, we have found that in 428 “cowtests” staphylococci werefound in 21 %. No clinical case was observed, although careful records of all abnormalities of udders and milks were kept.

The data which we have obtained show that staphylococcus infection accompanies changes of chemical composition which may be of importance in the preparation of milk products, but before categorical statements can be made more observations are obviously necessary.

1. Fluorimetric tests applied to commercially pasteurized and commercially sterilized milk showed that in the former some 10% and in the latter up to 50% of vitamin B1 was destroyed in the course of the heat treatment.

2. Riboflavin withstood both treatments without loss.

3. These findings are in satisfactory agreement with the results of earlier biological tests.

1. The application of the colorimetric dilution method for the determination of pH values in cheesemaking is discussed and the necessary precautions for accuracy described.

2. Bromthymol blue is recommended for milk and whey of pH. > 5·8 and the B.D.H. 4460 indicator for whey of pH < 5·8.

3. Titratable acidities and pH values each afford an incomplete picture of the working of a curd. Together they afford a valuable indication of the normality or otherwise of the making process.

4. The buffer value of whey rises steadily during manufacture. The pH rises abruptly after salting, although the titratable acidity continues to increase.

5. The buffer value of whey is controlled chiefly by the rate of working but tends to be lower with pasteurized milk.

6. A diagrammatic method for summarizing the “behaviour of a vat” and for detecting abnormal working is described.

Lyphan paper M 25 can be used for pH measurements in milk and whey in the pK range 5·4—6·6. As a rule the error does not exceed 0·1 pH.

In very acid milk and whey (pH < 5·4) lyphan paper of the L series may be used. Generally the deviation does not exceed -0·2 pH. In alkaline milk and whey lyphan paper cannot be used.

In milk and whey from cows infected with mastitis M 25 may be used unless the pH exceeds 7.