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butter fat high the other solids are present in a proportionately larger amount. Thus, Professor Cochrane, analyst to the Pennsylvania board of agriculture, gives the following results at 60 degrees F.:

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Hence, it is very properly concluded that the lactometer, or lactodensimeter, is an instrument of much value in testing a milk from the standpoint of adulteration. Thus, a milk of low specific gravity and low in solid constituents would indicate the addition of water; a milk of high specific gravity and a low percentage of fat is probably skimmed; and a milk having a low specific and yet a high percentage of fat indicates either a very good milk watered, or an unfair sample taken from the creamy portion of the milk.

From many thousand analyses made by Dr. Paul Veith, F. C. S., analyst for the Aylesbury dairy, London, England, during eight years, broad general conclusions have been drawn. During those eight years he analyzed 84,746 samples of milk, and has preserved records of great value, from which the following are some of the more important deductions: He found that the non-fatty solids are the most constant factors in milk, having the following relations to one another:

Total non-fatty solids.

12

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the milk sugar,
mineral matter (ash),

1. the nitrogenous matter (of this

being caseine).

* Per cent.

He likewise found that milk from cows fed with the same foods shows a remarkable constancy of specific gravity, rarely falling outside the limits of 1,030 to 1,034.

As regards quantity, he found that the morning milking stands in relation to the evening as 100 to 72, accounted for, he thinks, by the fact of the cows having before them water during the night, and no food after the evening meal. The great increase shows a difference in quality, but not of an amount to offset the difference in quantity. Thus, analyses made on eleven different days showed in one cow (a type of the others) that the amount of pounds of milk-yield averaged

14.4 pounds at morning milking,

10.2 pounds at evening milking.

Fat solids. 3.5 per cent at morning milking,
4.1 per cent at evening milking.

Non-fatty (9.13 per cent at morning milking,
solids. 9.32 per cent at evening milking.

That these results are constant, may be seen from similar experiments made at the Agricultural college, Guelph, Ont. The following are the results of the average of one week's examination, by Prof. C. C. James, of the milk of six cows by the Babcock tester to show butter fat:

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Dr. Veith further found that the quality of milk reaches its height in November, while in the spring months the poorest milk is received, with another depression in July. returns were gathered from thirty to fifty farms, and fresh

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milch cows are obtained at all seasons of the year. It would therefore appear that at these seasons the variations depend upon climatic changes, since the amount and kind of food consumed on the same farms are much the same throughout. There can be no doubt that an influence of an important nature is exerted by weather changes. Thus, a sudden fall in the barometer, and a raw easterly wind, will in twenty-four hours lessen the yield of one hundred cows by a number of gallons; and a sudden accession of severe cold will, for a day or two, notably lessen the milk-flow. Great heat in the summer similarly affects the milk-supply. But the most notable differences depend upon the kind, amount, and methods of feeding. The physiological factor, the perfect or imperfect metabolism of digested products, — in other words, the character of the soluble constituents of food entering the stomach and the digestibility of other foods, forms the most potent factor, under ordinary conditions, in influencing the amount and quality of milk. Ensilage of any kind will give to milk its special flavor, and produce a certain quality as regards richness and permanency; so also will such foods as bran and various ground grains; and the same is the case with brewers' grains, fresh or fermented; refuse starch-products, and so on to distillery slops.

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Now while there is no doubt that milch cattle become habituated to certain foods unnatural to them, yet the experience of close observers shows that milk always has a physiological normal constitution dependent upon the perfect metabolism of wholesome grains and grasses, and that other foods do produce in some degree abnormal products. All dairymen are aware of how leeks in spring-time flavor the milk, and dairymen are very well aware that so simple a thing as turning cows from permanent pasture into a clover-field will produce so notable a taste as to cause complaints of something having gone wrong in the milk.

This subject opens up a wide field for investigation, which as yet has received but little attention, even from the sanitary standpoint. From more or less general experience, the

impression exists that the milk of cows fed with refuse grains and ensilage, all including some starch or sugar more or less altered by the alcoholic or acetic ferments, has not the keeping properties of the milk of cows fed with hard grains and grasses. The diarrheal troubles in children have not infrequently been attributed to this cause. I am not aware of any extended experiments going to show that such milk contains an excess of sugar, and, as already mentioned, Dr Veith states from his many analyses that sugar maintains its average proportion of one half to the non-fatty solids of milk, and that these constituents maintain throughout a remarkable relative constancy. On many of the farms of the Aylesbury Company, brewers' grains are fed, but it may very well be that in the English climate fermentative changes are ordinarily slower than in the warm weather of this country.

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This point naturally brings me to speak of the acidity of milk, and its relations to normal physiological processes. are aware that milk is spoken of commonly as being a practically neutral secretion, giving slight reaction with both red and blue litmus-in other words, being amphioteric. reality, however, normal milk, owing it was thought to a certain amount of carbonic acid dissolved in it, ought to be considered as acid. Dr. Wynter Blythe by experiment has shown that milk contains, in a litre of fresh warm milk, 1.83 c. c. of gasescarbon dioxide, .06 c. C. or 3.27 per cent; nitrogen, 1.42 c. c. or 77.60 per cent; oxygen, 35 c. c. or 19.13 per cent; and that standing increases its carbonic acid by a certain amount of oxygen absorbed.

It is questionable, however, whether milk does really contain when freshly milked any appreciable amount of carbonic acid, since by experiments carried on in the laboratory of the provincial board of Ontario it has been found that the acid reaction found in milk just drawn does not alter on boiling, by which process carbonic acid would be driven off if present as a free acid. It has further been found that milk, if rapidly aerated and cooled, does not increase in its acid reaction.

The following results of experiments carried on in a large

dairy near Toronto by my laboratory assistant, Mr. J. J. McKenzie, will be found of great interest in determining this point:

The standard normal solution of caustic soda (40 grammes to I litre of water) was prepared, and added to milk just drawn from the cows into clean sterilized flasks. The point of acidity was delicately determined by pheno-phthalein having been previously added to the milk. It will be seen that the acidity of milk may be represented as having an average of 1.1 in a series of individual milks, or in the mixed milk from a herd of one hundred cows; that is, 1.1 cubic centimetres of normal caustic soda solution was necessary to neutralize the acidity present. As these cows had been fed month after month on fresh cut hay mixed with bran and pea-meal, and on the grass for a few hours each day, it may be said that the food was the best possible for determining what is the normal physiological acidity of milk. From the fact that carbonic acid does not seem to be a factor in this acidity, but that it depends upon some acid basic salts (probably phosphates) present, it will appear that in the determination of the acidity of milk we have a method of much value in not only testing the effects of different foods on milk, but in estimating the changes which go on in milk under the influence of bacterial ferments of various kinds.

At this point I enter upon a part of our subject so interesting and yet so intricate, that I confess to having some fears as to the propriety of my attempting to deal with it; and yet, I am convinced that until the biological factor in the study of milk has been followed with the same assiduity as has the chemical, we are not likely to greatly increase our present knowledge on the subject.

Starting then with the facts just related regarding the acidity of milk, I believe it will be found that, under ordinary conditions, the determination of the acidity of any milk will serve as a measure of the degree of bacterial infection which has taken place, and of its fitness for use as a food. For instance, in the experiments which I have recently been

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