The previous section of this study in which the titration curves of various milk constituents were discussed approximately denned their influence on the titration. Some of the conclusions arrived at are amplified and more clearly defined when the buffer index of the curves is considered.

1. The lactic acid flora of Cheddar cheese made from milk of certified quality form a well-defined, physiologically homogeneous group of bacteria, growing best over a temperature range of from 22 to 37° C. They may be classified into four well-defined types, Str. lactis, Str. cremoris, Sbm. plantarum and Sbm. casei, and have been studied over a period of five years. It appears from the evidence found that Str. lactis and Str. cremoris are distinct species, but that Sbm. casei and Sbm. plantarum represent different stages in the adaptation of a common progenitor to conditions in a ripening cheese. Both the streptococci and the streptobacteria appear to be unable to oxidise sugars and may thus be considered indifferent to molecular oxygen.

2. A study of their frequency distribution from the curd at making to an 18 months old cheese has shown that Str. lactis and Str. cremoris are equally viable during the first month, after which the rod forms begin to predominate, Sbm. plantarum and, later, Sbm. casei being found. The former lactobacillus is only found when the cheese is from 1 to 5 months old, the flora consisting entirely of Sbm. casei after this time. The general vigour of all strains decreases with increasing age of the cheese. There is a marked correlation between the shape of the cell, the viability of the organism in cheese and its resistance to acids and lactates.

3. The factors controlling the sequence of flora in Cheddar cheese are discussed. There is no evidence that titratable acidity, oxygen tension and differential carbon sources are responsible for the sequence. It is suggested that lactate concentration, the extent of protein degradation and osmotic pressure are factors responsible for the gradual replacement of the streptococci by the rod forms.

4. The significance of sugar fermentations by the lactic 'acid bacteria studied is discussed. The slow production of lactase is shown to be the reason for the slow growth of weakened strains in litmus milk.

5. Str. cremoris predominates over Str. lactis in the depth of the cheese in the early stages of ripening, whereas near the surface the reverse holds. Certain strains of Str. cremoris isolated from the depth of the cheese were particularly vigorous in growth in litmus milk, forming gas and beginning to peptonise the milk in about 3 days. Such strains consisted of very long chains of large cells of peculiar morphology. It is suggested that this finding is related to the known greater rate of ripening in the depth of the cheese.

1. Some account has been given of the cattle kept on the Government Farm at Samaru, Zaria, and of their management in the wet and dry seasons.

2. Figures extending over four seasons have been presented to show thatthe butterfat content of the milk produced on this farm is consistently higher in the morning than in the evening during the wet season, and that the reverseis true during the dry season.

3. The relative quantity of milk produced in the evening during the dry season is slightly less than during the wet season, but this difference is quiteinadequate to explain the change in the percentages of butterfat.

4. Some evidence is offered that this change in butterfat content is directly due to the marked climatic differences between the two seasons, and that it cannot be controlled by altering the diet of the cattle.

The reactions which occur when sour cream is “neutralised” with calcium hydroxide and sodium bicarbonate are discussed from the point of view of the acid-base equilibria.

Experimental results are recorded showing that:

1. When lime is the neutraliser, pasteurisation has little effect on the pH. or titratable acidity of the neutralised cream.

2. The reduction in acidity when lime is used is shown to vary from that calculated from the sodium hydroxide titration to an extent which depends on the pH of the neutralised cream. The reasons for and extent of this variation are defined.

3. When sodium bicarbonate is used as a neutraliser the loss of carbon dioxide (which is influenced by the method of pasteurisation adopted) has most influence on the degree of neutralisation obtained and the experiments show the extent of this at various acidities.

The variations in the pH-titratable acidity relationship of creams neutralised with calcium hydroxide and sodium bicarbonate are defined.

Details are given of two simple tests for efficiency of pasteurisation. The first, test A, may be carried out completely within half an hour, and will detect any gross errors of pasteurisation technique. The second, test B, is more searching, and will reveal minor errors of technique as follows:

(a) 1½° F. below the minimum temperature for pasteurisation, or (b) heating (at 145° F.) for 20 instead of 30 min., or (c) admixture of 0·25 per cent, of raw milk with properly pasteurised milk. Taken together, the two tests form an efficient method for the laboratory diagnosis of faulty pasteurisation.

The weekly samples of typical milk from a small herd of Shorthorn cows have been analysed for chlorine content and nitrogen distribution (ninety-six samples). Lactose has been determined in seventy-five samples and copper and iron in twenty-four samples. The results are tabulated and discussed.

The author is indebted to Mr A. Wagstaff for carrying out the determinations of lactose.

1. A technique for examining bulk milk, by cultural and microscopical means, for evidence of mastitis among the cows is described. To demonstratea light contamination with haemolytic streptococci, cultural examination of gravity cream is advocated, whilst, if much significance is to be attached to the actual count, whole milk should be cultured.

2. Forty–two samples of Certified milk from sixteen producers wereexamined, and twenty–four of these contained beta-haemolytic streptococci when whole milk was cultured. Twelve of these herds were examined on three occasions during fifteen months, and samples from only two were free frombeta-haemolytic streptococci at every test.

Attempts were made to eliminate the bacterial factor in Cheddar cheeseripening, through the agency of chloroform, and an assessment of the role of rennet was thus rendered possible.

After investigating the effect of chloroform and toluene upon the proteolytic action of rennet and trypsin in milk, the results obtained were applied in studies upon the ripening of cheese in the presence of chloroform. Cheese of normal manufacture was chloroformed at the salting stage or one week or more after manufacture (when the curd had lost its rubbery nature and the germicide was more easily incorporated). Owing to the weakened activity of enzymes in the presence of germicides, it was necessary to employ larger proportions than usual of rennet, measured additions generally being made at the time when the chloroform was added. Under these conditions the general course of protein degradation, as measured by determinations of soluble nitrogen and non-protein nitrogen, was found to be identical with that occurring in normal control cheeses. Strong evidence was thus afforded that rennet is the only important agent attacking cheese protein during the ripening process.

In the partition between the non-protein constituents of the normal and chloroformed cheeses, respectively, there were observed definite differences which tended to remain constant over the greater part of the ripening period. The relatively higher proportion of subpeptone nitrogen in the normal cheese was shown to be due, at least in some measure, to bacterial action.

Cheese ripened in the presence of chloroform developed no volatile acid, and no cheese flavour could be detected.

1. Analyses have been made of the wheys obtained at various stages in the manufacture of Cheddar cheese.

2. There is shown to be a steady rise in the concentrations of calcium and phosphorus in the wheys throughout the process up to salting. The calcium rises much more rapidly than the phosphorus.

3. After salting there is a sudden temporary fall in the concentration of both calcium and phosphorus in the whey, the calcium fall being particularly pronounced.

4. The concentration of calcium and phosphorus in the whey vary in accordance with the titratable acidity of the whey.

5. In normal cheese making some 60 per cent, of the calcium and 57 per cent, of the phosphorus in the milk is retained in the cheese.

6. Of the minerals lost in the whey some 86 per cent, of the calcium and 90 per cent, of the phosphorus escape before running.

7. An increase in the acidity of the milk before renneting increases the loss of minerals in the whey and reduces the calcium content of the cheese.

1. In an examination of the coliform flora of 114 specimens of bovine faeces, 342 cultures of coliform bacteria were isolated by the ordinary methods.Of the cultures obtained, 330 (or 96·4 per cent.) were typical Bact. coli andonly twelve (or 3·5 per cent.) were of Bact. aerogenes, Bact. cloacae and other Koser-positive types. The most prevalent types of Bact. coli were MacConkey's B, No. 71 or Bact. coli communior (185 cultures or 56 per cent.), MacConkey's B, No. 34, or Bact. coli communis Escherich (sixty-nine cultures or 20·9 per cent.), and MacConkey's B, No. 1 (twenty-three cultures or 6·9 per cent.).

1. Acetyl methyl carbinol and diacetyl are present in New Zealand butters made from slightly ripened cream.

2. Most of the carbinol + diacetyl found in such butters would appear to have been added with the starter to the cream, rather than developed during the customary mild ripening process.

3. Little change in the natural carbinol + diacetyl content of butter occurs during cold storage at 14—17° F. for more than 6 months.

4. Larger amounts of diacetyl (4 p.p.m.) added to butters made from cream with and without the use of starter, show considerable losses after several months' cold storage. The losses are of the same order, but, with the butters, made with starter, part of the diacetyl has merely been reduced toits precursor (carbinol) form.

1. The buffer values of wheys obtained at various stages of the cheesemaking process have been determined over the pH range 3·5—7·5.

2. The buffering between pH 3 and 5 is shown to be chiefly due to lactate, while that at higher PH values is chiefly due to calcium phosphate.

3. The results of the buffer determinations are shown to be in accord with the analyses of the mineral constituents of wheys reported in the first paper of this series (1).

1. Determinations of acidity, lactose and lactic acid were made at various stages during the souring of milk by starter cultures, both with and without the addition of a neutralising agent.

2. Throughout the fermentation, the increase in acidity of the milk was accounted for quantitatively by the amount of lactic acid produced.

3. In some instances in the early stages of the fermentation a considerable quantity of the lactose appeared to be converted to substances other than lactic acid.

4. Over the whole fermentation the amount of by-products produced from the lactose was small.

The coagulating enzymes employed in the manufacture of Cheddar cheese were varied in the following ways:

(1) Pepsin was substituted for rennet; two samples of somewhat different proteolytic action were used.

(2) The proportion of rennet normally employed for coagulating the milkwas doubled.

The use of pepsin resulted in cheeses in which the extent of protein degradationwas considerably smaller than in rennet control cheeses. The type of nitrogen partition observed was influenced to some extent by the proteolyticaction characteristic of the particular enzyme employed. The use of an increase dproportion of rennet led to the anticipated greater extent of protein breakdown, the type of nitrogen partition not being appreciably affected. Nodirect correlation was observed between the commercial quality of these cheeses and the extent or type of protein degradation which occurred.