Four grade Jersey cows were exposed for 7 hr. twice a week to each of several atmospheres having dry-bulb temperatures ranging from 85 to 110° F. and absolute humidities ranging from 6 to 16 gr./cu.ft. The following reactions were studied: rectal temperature; pulse rate; respiratory rate; respiratory volume; evaporative loss; calcium, phosphate and erythro-cyte composition of the blood; milk volume and butterfat content; behaviour.

Rectal temperature rose to higher values with less ready establishment of equilibrium the hotter the condition, but exceeded 107° F. only in the hottest atmosphere. (Dry-bulb temperature 110° F., absolute humidity 16 gr./cu.ft.)

Respiratory rate was similarly and markedly affected. In both cases, humidity had a marked effect as well as temperature, an increment of 0–4 gr./cu.ft. (approx. 4%) in humidity having the same effect as 1° F. rise in air temperature. The highest average respiratory rate was 200/min. Respiratory minute volume rose less than the rate, so that tidal volume was reduced.

Pulse rate was essentially unaffected by a rise in temperature but tended to rise somewhat with humidity.

Evaporative loss was markedly increased by temperature, much less so by humidity. Increased pulmonary ventilation was inadequate to account for the observed losses, which are attributed to sweat-gland activity.

Behavioural changes included some licking, panting, salivation, mild agitation, cessation of rumination and refusal of water. Weakness and staggers did not occur under these conditions.

Neither milk nor butterfat production was essentially affected by the exposures. Blood calcium and phosphate levels fell, but the erythrocyte count was unchanged.

These findings provide basic data with which subsequent observations under varying conditions can be compared.

1. During the first 2 weeks and last 2 weeks of a 9-week period nine cows, milked by machine, were prepared for milking by hosing and washing the udders with cold water 15 min. to 1 hr. before milking, while in the intervening 5 weeks the udders only were washed with water at 115 to 120° F. immediately before milking.

2. The hot-water routine had no pronounced effect on the yield and quality of the milk from the majority of the cows, although one reacted unfavourably to a change back to the cold water routine and had to be stripped by hand.

3. The gradual restriction, over an interval of 4–6 weeks, in the milking time from 100 to 60% of the previous normal flow period for three cows in mid-lactation had no great influence on the maximum rate of milk flow from the udder, even when hot-water washing of the udder immediately before milking was introduced late in the experiment. The maximum rate of flow was, however, reached slightly sooner after putting on the teat cups.

4. The restriction in milking time caused only a small reduction in yield as the flow during the latter part of the flow period had in any case been small.

5. The fat content of the milk of the cows whose milking time was restricted fell somewhat while the solids-not-fat content remained steady.

6. Washing the udder with hot water or restricting milking time showed no clear-cut effect on the incidence of mastitis.

Four grade Jersey calves were exposed for 7 hr. twice a week to each of several atmospheres having dry-bulb temperatures ranging from 85 to 110° F. and absolute humidities ranging from 6 to 16 gr./cu.ft. The following reactions were studied: rectal temperature; pulse rate; respiratory rate; respiratory volume; evaporative loss; calcium, phosphate, sugar and erythrocyte composition of the blood; behaviour.

Rectal temperatures rose rapidly to a higher level than was shown by cows under similar conditions, but maintained a steady equilibrium thereafter, except under the most severe conditions.

Respiratory rate responses resembled those of rectal temperature, the difference from those of cows being even more striking.

Humidity had relatively less effect upon the rectal temperature and respiratory rate responses of calves than of cows.

Pulse rate and tidal respiratory volumes were relatively unaffected, but minute respiratory volumes rose.

Evaporative loss per unit body weight resembled that of cows, except that humidity again had less effect. Pulmonary ventilation was inadequate to account for the observed losses.

Behavioural changes resembled those of the cows but weakness of the hind limbs was observed at rectal temperatures above 106° F. Blood calcium, phosphate, sugar and erythrocyte levels were not essentially affected.

Possible explanations for the lower thermal tolerance of calves, as compared with cows, are considered.

It has recently been claimed that in modern high temperature-short time pasteurization plant fluctuations in temperature of the order of 1° F./sec. are unusual and probably artefacts, and that an instantaneous drop is certainly fictitious.

It has, nevertheless, been shown that such rapid drops in temperature do in fact occur frequently in high temperature-short time plants of the type investigated. The plant investigated was not of the latest design incorporating devices for speeding up the control by injecting steam directly into the hot-water pipe.

Temperature changes of the order of those in question were first observed by Mattick & Hiscox(1) of the National Institute for Research in Dairying, who carried out tests on pasteurization plant using a small mirror galvanometer with a very short time constant. The maximum rates of change were, however, not observed.

The streptococci occurring in raw and pasteurized milks of varying purity have been investigated. The organisms were placed in five main groups by testing for the hydrolysis of arginine, growth at 45 and at 8–12° C, survival in milk at 63° C. for 30 min. (measured by a semi-quantitative plating method), action on litmus milk, and the ability to form CO2 from glucose (tested by a cultural method). The groups thus distinguished are:

(1) Organisms of bovine mastitis.

(2) Str. bovis and Str. thermophilus. A clear-cut separation of these species was not obtained by tests for growth at 50° C, the hydrolysis of aesculin, or the fermentation of maltose or salicin; but, with suitable precautions, action on both maltose and salicin provides a differentiation. Certain strains of Str. bovis differ from the typical form of that species in their ability to proliferate over a wider range of temperature and in higher concentrations of salt and methylene blue and in their failure to split aesculin.

(3) Str. lactis and Str. cremoris, which were differentiated by tests for the hydrolysis of arginine and ability to grow at 40° C.

(4) Str.faecalis and its varieties. Many of the strains are non-haemolytic but otherwise indistinguishable from Str. durans. The formation of acetoin from citrate and from glucose are common but not universal properties in the enterococcus group.

(5) Heterofermentative streptococci. The majority of the strains were identified as Str. kefir. Str. citrovorus, which was isolated only occasionally, was distinguished by its low maximum temperature (under 37° C), weak resistance to heat and by fermentation reactions.

Raw milk was found to contain Str. kefir, Str. lactis and the mastitis organisms more frequently than the other species. Str. thermophilus and Str. bovis were the dominant forms in freshly pasteurized milk. Pasteurized milk held at 10–22° C. until it became tainted yielded Str. kefir and Str. faecalis and, at the higher temperatures, Str. bovis and Str. thermophilus.

Tinned trays were artificially infected with Staphylococcus aureus in diluted milk and the dried surfaces disinfected by rinsing with sodium hypochlorite solutions.

Under the conditions described, which we believe approximate those on many dairy utensils which have been imperfectly cleaned, the pH of hypochlorite solutions was found not to be a very important factor in determining their germicidal efficiency. At pH 10 and 11, the solutions were equal to or slightly more efficient germicides than solutions at pH 7.

In the destruction of 99% of the organisms on the metal trays, a solution at pH 10, containing 200 p.p.m. available chlorine was about 7 times as rapid as one with 25 p.p.m. available chlorine.

A study of 799 cultures of staphylococci and micrococci, isolated mainly from milk, showed that according to their general character the strains could be arranged in a virtually continuous series. At one extreme is the pathogenic staphylococcus and at the other a thermoduric saprophyte. The series consists of three main groups:

(1) The staphylococcus group in which the organisms are sugar fermenters and relatively sensitive to heat. They are, mainly at least, parasites of the animal body. Four subgroups are distinguishable. In three ammonia is formed from arginine, and in two acetoin is formed from glucose. A test for acetoin production defines those mannitol fermenters which do not produce coagulase.

(2) An intermediate group in which the organisms are obligate aerobes and do not produce acid from sugars.

(3) The dairy micrococci, a group of thermoduric sugar fermenters which occur frequently on dairy equipment and in pasteurized milk. The group comprises two species conforming to Micrococcus luteus Cohn emend. Lehmann & Neumann, and M. varians (Dyar) Migula.

The application of the Schibsted fat aldehyde test for the routine examination of butter and butterfat is facilitated by the following modifications:

(1) Storage of the reagent at cool temperatures.

(2) Use of sodium metabisulphite instead of sulphur dioxide.

(3) Preparation of the standard colour at a lower pH

The value of the phosphatase reaction for controlling the heat treatment of milk is unquestioned, but the accepted method of estimating phosphatase activity, namely, the colorimetric method of Kay using the phenol reagent of Folin, has three disadvantages:

(1) The number of estimations that can be performed in a given time is limited.

(2) Errors in matching the tints may occur.

(3) Samples of milk may be accidentally contaminated with traces of phenol, and this will lead to too high a Lovibond value.

1. The special conditions of the cream trade are discussed. Keeping quality is a major consideration which influences all operations and it has been shown that unusually high bacteriological standards of handling are essential.

2. The requirements for bacteriological control testing are indicated, together with the limitations of existing standard methods.

3. A rough sorting test has been developed which permits sufficiently rapid estimation of the probable keeping quality of heat-treated cream and which is applicable to routine grading of numbers of individual units.

4. Data from 2558 samples of heat-treated cream are presented to show the relationship between the colony count, conform test, grading test, and keeping quality.

5. Possible sources of bacteriological contamination have been indicated by the examination of 2337 plant samples. Commercial processing methods are discussed and satisfactory practical methods of operation have been developed to ensure a minimal bacterial population.

6. The keeping quality of cream has also been studied in relation to the effects of cold storage before distribution and of exposure to atmospheric temperature during distribution.

The addition of 10% of sodium chloride to milk caused an average drop in pH of 0·42 unit. Different workers have found very variable relations between the pH of cream and the pH of salted butter churned from it. When 10% of sodium chloride is added to 0·2% solutions of sodium citrate or sodium phosphate there is a drop in pH of the order of 1 unit. When an alkaline solid phase is present as in the serum of neutralized cream and butter, and in milk, this change in pH may be diminished or reversed, possibly by increased solubility of the alkaline precipitate in sodium chloride solution. Factors are listed which will cause the pH of salted butter to differ from that of the cream from which it was made. In the churning of alkaline creams there occurs in the butter an increase in the proportion to the serum water of calcium phosphate and of other solids-not-fat.

The increased use of dried-milk products in human feeding during recent years stimulated investigations into and more rigid control of the bacteriological quality.

Spray-dried milk powder from the same eight British plants has been examined for bacteriological quality at this Institute in several different years and the results show the marked improvements which have been made.

1. A method is described based on wet-ashing in micro-Kjeldahl flasks for the accurate estimation of iron and copper in 10g. samples of butter or dry butterfat or in 5g. samples of cream.

2. An acid extraction method for the routine estimation of copper and iron in dry butterfat is described. This method is shown to give a reliable estimate of the quantities of the metals present.

3. A simplified method for the estimation of iron in cream and butter is described in which the iron is first freed from its protein complex by the addition of thioglycollic acid. Copper is estimated by a similar method, but without the addition of a reducing agent. Both methods give results agreeing reasonably well with the wet-ashing method and are suitable for the routine estimation of these metals in cream and butter.

1. Over 100 samples of roller-dried full-cream milk and rather less than 100 samples of spray-dried milk reconstituted and incubated for 20 hr. at 55, 37, 39, 22 and 15·5° C. have been examined by the methylene-blue or resazurin-reduction tests at 37° C. The results have been compared with the plate count at 37 or 30° C. of the freshly reconstituted milk and with the keeping quality at 15·5° C.

2. A range of reduction times suitable for routine use was obtained after incubation at 22° C., but the results showed a very poor correlation with plate count at 37 or 30° C. and with keeping quality.

3. After incubation at 55, 37 and 30° C. the reduction times were too short, often showed delayed end-points, and the milk frequently clotted during examination.

4. Results with resazurin were similar to those using methylene blue and no significant differences resulted from the two different methods of reconstitution.

1. Chemical estimations of carotene and vitamin A in New Zealand butters from two of the principal butter-making districts of the North Island during the seasons 1935–6 show that the total vitamin A potency was fairly high.

2. There were seasonal variations apparently due to nutritional rather than physiological causes. The minimum values (33–37 i.u./g. butterfat) for total vitamin A were found in late summer (February) at the time when the pasture normally tends to dry up, while the peak values (42–53 i.u./g. butterfat) occurred in late winter and spring (July-October). The variations in vitamin A potency with season were in the opposite direction to the variations recorded in the literature for Europe and America. The difference is no doubt due to the practice of stall-feeding in these countries in contrast with the all-the-year-round grazing commonly practised on dairy farms in New Zealand. The spring flush of grass is also later in the season in Europe than in New Zealand.

3. The more deeply-coloured Jersey butterfat was only slightly richer in total vitamin A potency than Friesian butterfat.

4. Contents of carotene and vitamin A in the fat of colostrum were very high, but reached normal values within 4 or 5 days after parturition.

1. Over 200 samples of spray-dried milks from eight British plants have been examined for total and spore counts, numbers of β-haemolytic colonies and for moulds, yeasts and conliform bacteria.

2. The mean count and standard deviation range for total and spore count are reported. No β-haemolytic colonies other than those due to spore-forming bacilli were detected.

3. After ageing the reconstituted milk for 24 hr. at 15–5° C. the mean count (37° C.) was unchanged; at 22° C. the increase was 2000-fold and at 37° C. the milk had clotted within this time.

4. The predominating organisms in a random selection of the reconstituted milks are described, both for the fresh milk and after ageing at 15·5 and 22° C. A marked increase i n spore-forming bacilli was noted at 22° C.

5. The relation of the flora of reconstituted milk to its food-poisoning potentialities is briefly discussed.

1. Three spray-dried separated milk powders with moisture contents of 2·9, 4·7 and 7·3% (3 hr. air oven) or 3·0, 5·0 and 7·6% (20 hr. vacuum oven) were packed in air and in almost pure nitrogen, in gas-tight cans, and stored at 20·0, 28·5 and 37° C, for a period of nearly 2 years.

2. The powders were examined at intervals for palatability, colour, pH, equilibrium relative humidity (indicating crystallization of the lactose), conversion of β-lactose to α-lactose hydrate, decrease in total soluble lactose, absorption of oxygen, production of carbon dioxide, solubility in water at 20 and at 50 or 60° C, changes in the distribution of soluble nitrogen, reducing power towards potassium ferricyanide, base-binding capacity, formol titration, weight of the undialysable fraction, free amino-nitrogen by the Van Slyke method, sugar attached to the protein, and bacterial content.

A Gram-positive, aroma bacterium, the so-called ‘malt coccus’, has been isolated from malty-flavoured starters. It coagulates milk most readily at 35–37° C. The ‘malt coccus’ differs from the aroma bacteria mainly in that it forms acetaldehyde from pyruvic acid, evidently through carboxylase. Acetaldehyde is the chief factor in the formation of malty flavour. The ‘malt coccus’ sours milk feebly. If starter is heavily contaminated with the ‘malt coccus’, the acidity (SH°) is reduced but the aroma reaction (V.-P.) increases. The malty flavour persists in the starter during transfers and becomes more marked with rising temperature. The ‘malt coccus’ retains its aroma-forming ability for long periods in the laboratory.

1. A simple method of determining the acid degree of cheese fat has been described.

2. An average value of fat acidity on a series of thirty-eight samples of experimental Canadian first-grade Cheddar cheese, covering a period of about a year, has been eatablished at 1·0 ml. N/10 NaOH per 10 g. for cheese 2–4 weeks old.

3. An average acid degree for four experimental cheese from pasteurized milk was found to be 0·6.

4. A high acid degree was obtained on cheese fat made from milk in which lipase action was induced by vigorous agitation; the longer the period of agitation the higher was the acid degree. Extensive lipolysis took place at some stage before the cheese was removed from the press. Subsequent increase in acid degree was slight.

5. Fat acidities on a series of commercial Cheddar cheese, selected so as to include a high proportion of cheese degraded for unclean and rancid flavour, ranged from 1·2 to 4·6 with two exceptionally high values of 24·8 and 26·5. The incidence of undergrade cheese increased as the acid degree increased. All cheese with an acid degree of 2·8 or higher were below first grade on flavour.

6. Cheese made from milk, in which acid was developed by the addition of a small amount of starter the night before and which was partly homogenized, showed a high acid degree although the flavour was quite good—often first grade. Similar cheese, but with 3% starter added in the morning, showed only slightly higher fat acidity and scored lower for flavour. These findings cannot be explained as a simple inhibition of the action of milk lipase by acid development.

The reaction of casein and of fresh and deteriorated milk protein with nitrous acid has been followed at constant temperature for 4 hr. in the manometric apparatus of Van Slyke, and simplified procedures suggested whereby the method can be utilized for investigation of the deterioration of the protein of separated milk powder during storage.

Technical assistance in this work was given by Mr L. J. Parr: The work was carried out as part of the programme of the Food Investigation Board of the Department of Scientific and Industrial Research.