The results of the present experiments and of those reported in the previous paper(1) may be summarised as follows:

1. When minimal quantities of protein are fed in the production rations of milking cows, a deficiency of either lysine or tryptophane will lead to a marked reduction in milk yield. There is, however, some evidence of the storage of reserve N, which can be utilised when the food protein is inadequate.

2. The feeding of a lysine- or tryptophane-deficient ration causes a marked increase in urinary N, indicating a poor utilisation of food protein. On the other hand, the feeding of a ration containing adequate quantities of these essential amino acids reduces the urinary N, indicating efficient protein utilisation.

3. The utilisation of body tissue in an attempt to maintain normal milk production on a deficient protein ration is shown by the high creatine excretion. The fact that the S: N ratio of the excess sulphur and nitrogen excreted during the deficient protein periods approximates that of body tissue (circa 1: 15·7) confirms this conclusion.

1. Of 21,569 samples of mixed cow's milk taken under fair conditions of cleanliness and examined by means of the coliform test, 48·3 per cent, gave negative results with 1/10, 1/100 and 1/1000 c.c. amounts; 21–4 per cent, gave positive results with only 1/10 c.c.; 14·0 per cent, gave positive results with only 1/10 and 1/100 c.c.; and 16·3 per cent, gave positive results with 1/10, 1/100 and 1/1000 c.c. It is probable that these results are better than those generally obtained.

2. The proportion of coliform-positive samples was much higher in summer and early autumn than during the winter and spring. This seasonal variation was largely due to atmospheric temperature, there being a well-marked direct correlation between the proportion of coliform-positive samples and the mean of the minimum and maximum atmospheric temperatures.

3. Of 21,857 samples examined, 10,458 were coliform negative and had an average bacterial content of 25,294 per c.c; 11,399 were coliform positive and had an average bacterial content of 160,577 per c.c. The coliform-positive samples contained on an average 6·3 times as many bacteria as the coliform negative.

1. A comparison has been made of the accuracy of the ordinary plate and Burri smear-culture methods for the determination of the bacterial content of milk samples.

2. In determinations made by the smear-culture technique the percentage error has been shown to be markedly higher than in those made by plating.

3. Evidence is presented in support of the view that the inaccuracy of the Burri method (as ordinarily employed) when compared with the plate technique is partly due to the errors involved in loop measurements and partly to the inferiority of the conditions for growth on slopes to those in plate cultures.

It is well known that the quantity of salt added to Cheddar cheese curd has an important influence on the quality and rate of ripening of the resultant cheese. The character of the cheese body is, indeed, dependent to a large extent on the rate of salting. An investigation of the salt content of cheeses of tender body, normal body, and harsh body showed that the percentage concentration of salt in the moisture in cheese of normal body in general did not exceed 5·5 per cent. (1).

The heating of milk causes denaturation of the lactalbumin and lactoglobulin to an extent depending on both the temperature and the time of heating.

A series of data has been given for the amounts of albumin and globulin denatured on heating samples of milk at various temperatures from 63 to 80° C, for periods of from 2½ to 60 min.

An average of 10·4 per cent, of the total soluble protein was denatured after 30 min. heating at as low a temperature as 63° C.

Smooth curves were obtained for the progress of denaturation with time at each temperature, and, over the range of 63–75° C, the relative increase in velocity of denaturation for each rise in temperature of 1° C. was found to be constant, the temperature coefficient of the reaction being 1·5.

1. Using the method described by Sanders for protein and fat precipitation from cow's milk, a fairly satisfactory method of determining the phosphorus partition in cow's milk has been devised.

2. It is found that the gravimetric procedure of the American Association of Official Agricultural Chemists ((10), p. 3), which was not, in any case, specifically recommended for the analysis of milk, cannot be applied with safety to the determination of inorganic phosphate in filtrates prepared by Sanders' (1932) method, and that the conclusion that there is no appreciable amount of organically combined phosphorus in these filtrates is therefore invalidated.

3. The ester P (organically combined, acid-soluble P) in milk obtained by the usual milking routine varies from 1/7 to 1/4 of the inorganic P of the milk (from 7 to 21 mg. P per 100 c.c. milk).

4. An active phosphatase is present in cow's milky, and brings about changes in the ester P content of the milk on standing, possibly within and certainly without the mammary gland. Like phosphatases of all mammalian tissues, its optimum pH is in the neighbourhood of 9·0. In freshly drawn milk it is working, therefore, considerably on the acid side of its optimum.

5. The phosphoric ester P of the milk appears to vary with the breed of cow, being low in the miiy of Canadian Holstein-Friesian cows and higher in that of Jersey cows.

A method is described for the quantitative determination of phosphatase in raw milk. Using this method, it has been found that phosphatase is sufficiently thermolabile to be destroyed completely by pasteurisation if this process is properly carried out. The absence of phosphatase from a sample of milk or cream indicates with a fair degree of certainty that the milk or cream has been heated sufficiently to destroy such pathogenic organisms as were originally present, though it is of course no guarantee that the product is free from these organisms at the time of testing.

A simple, qualitative test-tube method is described which may be used for differentiating between raw and heated milk, or between raw and heated cream, and which with slight modifications may also be used for distinguishing between butters made from raw or from heated cream.