One fact emerges from a consideration of the literature upon the methods at present in use for determining the bacteriological content of milk, viz. no one method is capable of giving exact information as to the numbers of living bacteria present.

The plate count has been shown to be subject to a number of limitations to its accuracy, but it is possible that these are much more the result of failure to appreciate the importance and effect of observing the protocols of a standard technique, than of insurmountable causes of error inherent in the method. Any one laboratory should be able to return results which are comparable from sample to sample, but as has been shown, it is unlikely that results will agree between laboratory and laboratory unless the most rigid precautions to secure uniformity are enforced. This latter fact does not seem to be of very great importance, since the most that can be expected is that results shall reflect the condition of the milk at the time of examination. These will be governed by the previous history of the milk. Figures have been given which show (p. 120) that, if milk is properly produced and handled, the bacterial content will be, even 24 hours or more after milking, within the range where the plate count as a method of computation is more reliable than any other known method.

From the point of view of keeping quality and value for some manufacturing purposes, milk is either good or bad, and the obvious inaccuracy of the plate or any other method is a matter of small importance when the bacterial content has once exceeded 500,000 per 1 c.c.

Nevertheless there is no sort of justification for attempting to separate milk into classes, which are not broad enough to include the variations which have been repeatedly shown, although not always on sound lines, to occur in the figures. It may be possible so to separate milk of very low bacterial content, but it is not possible to do so when the bacterial content exceeds, say, 200,000 per 1 c.c. It must always be remembered that the colonies appearing on agar plates arise from groups as well as from individual bacteria.

In view of the fact that keeping quality, the basis on which the consumer judges milk, depends upon the kinds as well as upon the numbers of bacteria, it appears wise to supplement bacterial examinations with determinations of keeping quality, and, in view of their special significance, of organisms of the coliform group.

It seems that, although the methods of Breed and Frost are excellent for rapidly classifying milk into broad grades, their accuracy is necessarily diminished by their very nature, in that the results obtained are dependent upon computation to a greater extent than the plate method and, although it is possible to secure good results, the time consumed in getting these is as great, if not indeed greater, than by the plate method.

The reductase test, although it has a large sphere of usefulness as a factory method, will not give accurate information as to the numbers of bacteria in milk.

It has been observed that media containing tissue extracts promote pigmentation of the organism causing “rusty spot” in cheese. Growth, but not pigment, may be obtained in a medium containing a fermentable carbohydrate and a suitable protein digest.

The substance in tissues promoting pigmentation has properties similar to those of vitamin B.

In addition to these chemical requirements, moisture and surface in a medium greatly stimulate pigmentation.

Pigment is only produced when the medium is at an oxidation-reduction potential below that at which litmus is reduced.

The following factors appear to govern the growth and pigmentation of this organism: (1) a certain range of oxidation reduction potential; (2) moisture; (3) surface; (4) a fermentable carbohydrate; (5) a minimum concentration of soluble available N; (6) a factor closely associated with, but not identical with, vitamin B1.

Certain properties of the factor are described.

The relation of this investigation to “rusty spot” in cheese is discussed.

1. With a view to a chemical study of the ripening of cheese made from raw and from pasteurised milk, two sets of three loaf Cheddar cheese were made from clean milk and from market milk respectively, so that in each set there was one cheese made from raw milk, one from milk flash-pasteurised at 165° F., and one from milk flash-pasteurised at 185° F.

2. Analyses of the whey drawn from each cheese showed a tendency, especially with market milk of lower hygienic quality, for pasteurisation to cause more of the soluble milk proteins to be incorporated in the cheese.

3. When acidity developed rapidly in the whey after cutting, the resulting cheese was depleted of a proportion of its mineral constituents.

4. The cheese made from pasteurised milk developed a bitter flavour, which was very pronounced in those made from the milk heated to the higher temperature.

5. The chemical analyses showed that in both sets, pasteurisation reduced the quantity of ultimate decomposition products which were formed during the process of ripening.

The experiments recorded here were carried out at the National Institute for Research in Dairying, Shinfield, Reading. The author desires to express his appreciation of the facilities which have been placed at his disposal and of the interest that has been taken in the work by various members of the staff, in particular by Miss D. V. Dearden (who was responsible for the making of the cheese), Capt. J. Golding, and Dr R. Stenhouse Williams. Acknowledgment is also due to Prof. Wm Riddet, Dairy Research Institute, New Zealand, who suggested the desirability of an investigation of this nature.

The Australian dairy industry has in the past made remarkable progress in certain areas where the rainfall is conducive to the production of good natural pasturage. As long as land prices remained reasonably low, dairying was a fairly profitable form of primary production on the better soils in the regions of high rainfall. These are chiefly found on the seaward side of the Great Dividing Range which stretches from Queensland to Western Victoria. Later, irrigation areas suitable for dairying were opened in the Murray basin and still later the south-western corner of the continent has seen extensive dairying areas developed. In each State the industry evolved on its own lines and the degree of control over the various stages of the production of butter and cheese exercised by the respective State Departments of Agriculture differs considerably. In some States the main effort has been in the direction of control of the dairies; in others the factories have received most attention. Again, in other regions legislative control is still rather weak.

The possibility that some of the factors governing the inheritance of milk might be inherited in a sex-linked manner has been suggested by one of the writers. The need was felt for further investigation. There are two main avenues by which this question may be explored: by planned experiment with cattle or by a study of the existing milk records. The former method is slow and very costly, but would probably give conclusive results. The latter does not require experiment to provide the necessary facts, but the data may be somewhat vitiated by lack of control over conditions of nutrition and husbandry which undoubtedly affect, to a great extent, the amount of milk which a cow may yield in a lactation.

The story of our knowledge concerning the causes of undulant fever depends upon a study of three separate diseases, namely, Malta fever, abortion in cattle and undulant fever itself, which were not supposed to be related one to another. As time has passed, however, a very close relationship between these diseases has been found to exist.