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.

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.

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.

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.

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 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. 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. 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.

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.

‘Dry’, dialysed milk protein was stored for 6 months at 37° C. and 55% relative humidity alone and in the presence of small proportions of glucose, of high proportions of lactose and of sucrose, and of mixtures of these sugars.

The reducing sugars combined with free amino-groups of the protein, apparently in a 1:1 ratio; sucrose did not. The reaction did not proceed to completion, probably owing to difficulty of access of the reactive groups to one another. Only when the sugar-amino reaction occurred did discoloration ensue.

Glucose reacted more rapidly with the protein than did lactose, and the complex formed became discoloured and insoluble in both cold and hot water much more rapidly.

Sucrose and lactose both greatly delayed the onset of glucose-induced insolubility, lactose being the more efficient of the two. They did not prevent discoloration.

The protein alone became insoluble in cold but not in hot water after prolonged storage; but did not discolour. This change was prevented by sucrose. The behaviour of lactose was inconsistent, loss of solubility being accelerated in one experiment and retarded in another.

Iodine values, Reichert values, saponification values and softening points of butterfats from butters collected at monthly intervals over a period of 4 years from 9 factories representative of the main butter-producing districts in New Zealand were determined. The trend of variation of any one property throughout the season was remarkably uniform, both for different factories in the one season, and for any one property in the four seasons. Weighted monthly average iodine values, Reichert values, saponification values and softening points for the butterfat from all factories over 4 years were 36.7 (33.8–40.2), 30.4 (25.5–32.3), 229.5 (225.5–232.7) and 33.1 (32.2–33.7) respectively. The minimum iodine value occurred in midsummer, i.e. at the season of the year when maximum values are reported for northern hemisphere butters. The iodine values for South Island butterfats diverged markedly from those for the North Island butterfats during the winter, i.e. at the time when turnips are fed to cows in the South. In spite of these lower iodine values, the softening points of the South Island butterfats were lower throughout the year.

Cheesemaking experiments were carried out to investigate the moisture-retaining characteristics of curd made from milks of varying fat and casein content. The results indicate:

(a) That milk fat helps to retain moisture in a cheese curd. The higher the proportion of fat present the more drastic the treatment required in the cheese vat to reduce the moisture content of the finished cheese to the desired level. A higher cooking temperature, more dry-stirring of the curd and a larger proportion of salt are all necessary with rise in fat content of the curd.

(b) That curd formed from milk of a low-casein content (from Friesian cows) retains moisture in the cheesemaking process more tenaciously than curd from milk of a highcasein content (from Jersey cows).

1. Inhibitory strains of lactic streptococci have been encountered amongst strains of Str. cremoris isolated from starter and amongst strains of Str. lactis, isolated from sour milk, which had otherwise been regarded as suitable for cheesemaking.

2. Methods are described for determining the concentration of inhibitory substance produced and the effect of these inhibitory strains on a wide selection of lactic streptococci.

3. The significance of the presence of strains of lactic streptococci having inhibitory properties, if incorporated in starters, particularly when the strains are prepared separately and mixed in the vat, is discussed. Recommendations for the exclusion of inhibitory strains from such starter mixtures are made.

1. 277 strains of lactic streptococci isolated from commercial starters and 72 ‘wild’ strains from souring milk, suitable for cheesemaking, have been identified. All the starter strains examined were Str. cremoris and those (with two possible exceptions) from sour milk were Str. lactis.

2. Since the strains from each source were so similar, the information obtained did not help in the selection of the strains, within each group, most suitable for starter.

3. It is suggested that three differential tests are sufficient to distinguish Str. lactis and Str. cremoris and to identify them when isolating strains suitable for starter.