There appears to be a west to east cline in the four north Wales counties in: (i) the proportion of calves sold during the autumn months September to December; (ii) the proportion of December milk sales in relation to the September sales; (iii) the proportion of the dairy and breeding herd in milk during the winter; (iv) the quarterly rates of conception in heifers during the period 4 December to 4 March. There does not appear to be any relation between percentage winter milk production and percentage tillage area in this region. It is postulated that the west to east cline is dependent mainly upon factors other than husbandry and that climatic conditions, particularly the hours of bright sunshine during the winter months, have a marked influence upon the breeding performance of cows and heifers during the period December to March.

This investigation has formed part of the survey of animal health and production in Wales, and thanks are due to the scientific branch of Messrs Cooper, McDougall and Robertson, Berkhamsted, for financial support. Grateful acknowledgement is made to the Ministry of Food, Colwyn Bay, for readiness in providing data and helpful advice; to Messrs Pritchard, Auctioneers, Bangor, and Messrs Beardmore, Auctioneers, Abergele, for permission to examine their records; to the Milk Marketing Board for providing the data on milk sales; to Profs. A. N. Worden and E. G. Bowen for the interest they have taken in the work.

Regular testing at 3-monthly intervals for periods extending to 7 years of some 650 to 850 cows in fourteen herds indicated that the majority of the new infections caused by Sir. agalactiae were recorded in the autumn months, August, September and October.

When infections were considered in relation to the stage of lactation, although higher new infection values were recorded at the first test after calving than at later stages, the differences were not statistically significant.

We are indebted to Dr D. N. Lawley for advice on the statistical interpretation of the results of this investigation.

Acknowledgement is also made to the Agricultural Research Council for grants in aid of the investigation.

Penicillin in milk inhibits the growth of some contaminant organisms and thus may have a variable effect in the reductase test for milk quality.

A variety of lactic streptococcus which is unusual in its growth requirements is described. The culture grows on an agar medium (based on B.D.H. peptone) only under conditions of semi-anaerobiosis. It will grow on the surface, however, if the medium is altered in certain respects, for example: (a) if the B.D.H. peptone is replaced by tryptone, the only peptone which appears to stimulate rapid aerobic growth of the organism; or (b) the lactose in the medium is replaced by glucose; or (c) the pH of the medium is reduced.

Different metabolic mechanisms appear to be involved according to the composition of the medium.

The culture is more sensitive to changes in milk composition than are other strains of lactic streptococci.

1. Streptococcus lactis cultures were found to vary considerably in their morphological characters when grown in raw and heated milk.

2. This variation in morphology was found to be the main cause for the difference in colony counts between inoculated raw milk and milk heated to 70° C. for 1 hr. over a 6 hr. incubation period at 37° C.

3. Similar T.M.C.'S on inoculated raw and heated milk during incubation at 37° C. explained why the methylene-blue reduction times were the same.

4. It is thought that denaturation of protein may be responsible for the production of short chains in heated milk.

5. The by-products of growth of Str. lactis are responsible for the production of short chains in raw milk after a long incubation time at 37° C.

1. The present position in the problem of ‘slow’ starter due to phage lysis has been reviewed.

2. The sources of some 450 strains of lactic streptococci, collected from a wide field, are given. The methods used in their selection for use as starter together with storage conditions, suitable to maintain their activity, have been discussed.

3. The sources from which phages for the lactic streptococci have been obtained and the methods of ‘building up’ a phage of high titre from dairy products, have been discussed. Attempts have been made to isolate phages from pig-faeces, after feeding starter strains to pigs, to adapt phages to strains previously unattacked and to establish interrelationship of the phages and strains of lactic streptococci with phages and strains of enterococci.

4. The strains of lactic streptococci have been classified in eleven phage types by modifying a method described for the phage typing of staphylococci. Identification of a type has been based on the reactions of a ‘phage pattern’ and not on the reaction of a single phage. It has not been possible to adapt one phage to lyse all the strains of one type and to replace the several phages on which type identification originally depended but, adapted phages have indicated the subdivision of some types.

5. The application of the ‘phage-resistant carrier’ strain phenomenon to phage typing has been investigated. The results have helped in the typing of some strains.

6. Phages used in typing the strains have been classified by means of antiphage sera, prepared from a selection of the test phages. On the data presented the majority of the phages were divided into three groups and the results have been discussed with reference to the phage types suggested.

7. The significance of phage typing, adaptation of phage and phage carrying in the selection of starter strains has been considered and the best method of applying this information to the control of ‘slowness’ in cheese factories has been discussed.

A method is described for the colorimetric determination of lactic acid in milk and unsweetened milk products. The protein and lactose is removed after precipitation with copper sulphate and calcium hydroxide at 45° C, the lactic acid in an aliquot of the filtrate is oxidized to acetaldehyde in sulphuric acid in the presence of copper sulphate, a purple colour is developed with p–hydroxydiphenyl, and the colour intensity is measured in a photoelectric absorptiometer or other suitable instrument.

Recoveries of from 96 to 103%, averaging 100%, were obtained when 20–400 mg. lactic acid/100 ml. were added to fresh milk.

The proposed method has an advantage over existing methods in the ease and speed with which large numbers of determinations can be carried out simultaneously whilst retaining the essential accuracy.

The milk of 100 cows and of the same number of buffaloes, in Cairo and its neighbourhood, was analysed; analyses were also made on bulk samples taken at 2-week intervals from the milk of the two buffalo and cow herds of the Faculty of Agriculture at Giza. All samples were mixtures of morning and evening milkings in proportion to yield.

The Bird & Derby method of calculating percentage butterfat loss in buttermilk is in error because it assumes that all the buttermilk in the granules at draining is retained in the buttermilk, whereas much of it is washed out in the wash water. Lactose estimations in butter and buttermilk confirm Udy's finding that butter contains about 10% of buttermilk. The Udy formula, viz.

is therefore in this respect correctly based and can be applied to individual churnings of butter in the same way as the Bird & Derby formula has been applied. The Bird & Derby formula should be discarded except for use when the granules are not washed with chill-water.

Both the Udy and the Bird & Derby formulae do not allow for the content of fat in the buttermilk retained in the butter or for the influence of fat content of the buttermilk on the calculated quantity of serum lost. When these factors are taken into account the Udy formula becomes

The correction +0·0012f F is not significant.

Penicillin present in cheese milk affected the performance of various ‘single strain’ starter cultures in the cheese vat.

A concentration of 0·07 penicillin unit/ml, in the milk was sufficient to cause a complete failure or ‘dead’ vat with the most sensitive strain of Str. cremoris. Two strains ceased to produce acid in the later stages of the manufacturing process when the milk contained 0·10 unit/ml. With three other strains the 0·10 unit/ml, level delayed acid development; the experimental vats required 20–40 min. longer than the controls to reach ‘salting’ acidity.

Flash pasteurization temperatures usually employed in cheese-making (150–160° F.) did not appreciably alter the activity of penicillin in the cheese milk.

The quality of the cheese produced was influenced by the rate and extent of acid production by the starter cultures in the vat during manufacture.

Experience in the field indicates that where a large number of cows are treated simultaneously for mastitis, there may be sufficient penicillin in the cheese milk to affect the starter, if the milk from quarters undergoing treatment is included in the bulk milk.