Details are given of a semi-micro Kjeldahl method for the determination of the total, casein, albumiij, globulin, proteose-peptone, and non-protein nitrogen of milk. The method is accurate, rapid, and particularly suitable for the determination of the smaller nitrogen fractions.The various nitrogen fractions are separated by the improved procedures described in the preceding paper.

It has been known for many years that organic acids are produced by bacterial fermentation in the rumen. T h e importance of such fermentation in the nutrition of the ruminant has been adequately appreciated only recently, with the establishment of the relative proportions in which the acids are produced and the discovery of their role in ruminant metabolism.

With 1 Figure) IN a previous paper (l) it was shown that secondary proteins of a proteosepeptone nature are present, with albumin and globulin, in the soluble protein fraction of normal cow's milk. In the present paper improved methods are described for the precipitation and determination of all the milk proteinscasein, albumin, globulin and the proteose-peptone substances. The methods should prove of value on account of the importance of a detailed and accurate knowledge of the protein distribution in studies of milk composition, and of the physiology of normal and abnormal milk secretion.

This work is a continuation of our earlier studies on the effects of commercial processing methods, as used in Britain, upon the nutritive value of milk(i-i3). It had two main objectives: one was to add to the existing knowledge by including measurements of factors which were either unknown at the time of the earlier investigations or for which satisfactory methods of measurement other than biological have only recently been evolved; the other was to study the effects of new methods and recent modifications of existing ones.Of late the general trend in milk processing has been towards the application of increasingly higher temperatures for short periods of time in various pre-treatments and also towards the use of high temperature in the main treatments themselves. In view of the heat lability of many nutritionally important constituents of milk, the nutritive effects of these new methods obviously demanded study.The paper deals with, seven vitamins of the B complex in seven heat-treated milk products made from one bulk of raw milk. METHODS Bulk milk.A bulk of 170 gal. of whole milk predominantly from Shorthorn and Friesian cows was obtained from a commercial dairy within 20 miles of the Dairy Department of Reading University. There it was emptied into an insulated stainless steel tank fitted with a mechanical agitator, and stored overnight at about 5° C. After thorough mixing, samples were withdrawn for processing when the milk was between 24 and 36 hr. old. With the exception of the ultra-high temperature (U.H.T.) sterilization, which was done at the National Institute for Research in Dairying, all treatments were done at the Dairy Department of Reading University on a commercial or pilot-plant scale.Pasteurized milk (H.T.S.T. process). Eighty gallons of milk were pasteurized at 72° C. (holding for 15 sec.) in a commercial A.P.V. plate-type heat exchanger and the milk was sampled after having been cooled to about 5° C.Sterilized milk (in-bottle process). Four gallons of milk were brought within 10 min. to 71-1° C. and then homogenized at a pressure of 2500 lb./in-2 and dispensed into pint bottles which were sealed immediately with ' Crown' corks of the type normally used. The bottles were heated in a steam autoclave for 30 min., some at 107-2° C. and others at 111° C. 192 Milk processing and some vitamins of the B complexSterilized milk (U.H.T. process). Fifty gallons of milk were brought within 18 sec. to 85° C, homogenized in a two-stage homogenizer at 500 and 2000 lb./in. 2 within about 23 sec. and sterilized by the ultra-high temperature process in an A.P.V. 200 gal./hr. HX plate-type stainless steel commercial plant. The milk was heated in it within 18-5 sec. to 135° C. and held at this temperature for about 2 sec. before cooling to 20° C. One gallon of this processed milk was dispensed into pint bottles, which were then sealed with ' Crown' corks and heated to 107-2° C. for 20 min. The second sterilization was necessary to simulate commercial conditions in which there is still no satisfactory method for a...

Most of the scanty literature on the major constituents of sow's milk is old, and nothing has to our knowledge been published on its vitamin composition, with the exception of the fragmentary information about vitamins A and C mentioned below.Probably the main reason for this relative lack of information is the difficulty of obtaining satisfactory samples of sow's milk. This difficulty is stressed in every paper published on the subject, and is connected with the mechanism of the 'let down' o f . milk over which the sow appears to have complete control. It is well known that milk cannot be obtained from the sow by milking in the way normally effective with other large animals. Small samples of milk have been obtained mainly by subterfuge. For this purpose a piglet had to be quietly removed while the sow was suckling her litter and the vacated teat quickly milked by hand. Elly & Petersen (1941) have lately devised a method for inducing the 'let down' of milk in the cow by the injection into her blood stream of the oxytocic principle of the pituitary. We have applied their technique to the sow with very satisfactory results, and have been able to obtain with ease from a number of sows large samples of milk at intervals throughout lactation. These samples have been analysed for major constituents and also for certain vitamins. We also obtained colostrum from the same sows in a way previously described (Braude, Kon & Thompson, 1945-6) for comparison of its composition with that of the milk. The investigation has covered the winter as well as the summer feeding of the SOW, and has included a study of the effect of season and fodder on the composition of colostrum and milk. Biological tests with guinea-pigs were also done to confirm the extraordinary richness of sow's colostrum in ascorbic acid reported in our earlier paper (Braude et al. .