MILK

Owing to the very important sanitary relations of milk as a model
food, the subject of its sophistication has during the past ten years
received particular notice at the hands of the food-chemist. The
investigations of our public sanitary authorities have shown that milk
adulteration is exceedingly common. It is stated upon good authority
that until quite recently (1883) the 120 millions of quarts of milk
annually brought into New York city were intentionally diluted with
40 millions of quarts of water, the resulting product rivalling in
richness the famous compound once lauded by the philanthropic Squeers.

The results of the examination of milk instituted by the New York State
Board of Health are given below, in which, however, the specimens of
skimmed milk are not included:–

——+——————-+——————–+————–
Year. | Number of Samples | Number showing | Per cent. of
| tested. | addition of Water. | Adulterated.
——+——————-+——————–+————–
1880 | 1514 | 167 | 11·0
1881 | 1110 | 51 | 4·6
1882 | 1775 | 120 | 6·7
——+——————-+——————–+————–

From October 1883 to March 1884, of 241 samples of milk examined by the
Public Analyst of Eastern Massachusetts, 21·37 per cent. were watered;
of 1190 samples tested during the year 1884, 790 were watered.[18]
Over 73 per cent. of the milk supplied to the city of Buffalo in
1885 was found to be adulterated. A very marked improvement in the
quality of the milk received in New York city has taken place since the
appointment of a State Dairy Commissioner (1884). Under the direction
of this official the metropolitan milk supply has been subjected to a
most rigid inspection, and with very satisfactory results. During the
years 1884 and 1885 nearly 45,000 samples of milk were examined.

A very common sophistication practised upon milk consists in the
partial or complete removal of its cream. This process of skimming is
conducted at establishments called “creameries,” of which sixty-three
were formerly known to send their impoverished product to New York
city. The State Dairy Commissioner has likewise accomplished much
towards stopping this form of adulteration.

Milk is the secretion of the mammary glands of female _mammalia_. It is
an opaque liquid, possessing a white, bluish-white, or yellowish-white
colour, little or no odour, and a somewhat sweetish taste. At times
it exhibits an amphigenic reaction, _i. e._ it turns red litmus blue
and blue litmus red. From the examination of nearly one thousand
cows in the States of New York, New Jersey, and Connecticut, the
_minimum_ specific gravity of milk was found to be 1·0290, the
_maximum_ being 1·0394. The opacity of milk is only apparent, and is
due to the presence of fatty globules held in suspension; these under
the microscope are seen to be surrounded by a transparent liquid.
Upon allowing milk to remain at rest for some time it experiences
two changes. At first, a yellowish-white stratum of cream rises to
the surface, the lower portion becoming bluish-white in colour and
increasing in density. If this latter is freed from the cream and
again set aside, it undergoes a further separation into a solid
body (_curd_), and a liquid (_whey_). This coagulation of the curd
(_caseine_) is immediately produced by the addition of rennet, and of
many acids and metallic salts.

The essential ingredients of milk are water, fat, caseine, sugar
(lactose), and inorganic salts. The following table, collated by
Mr. Edward W. Martin,[19] exhibits the results obtained by numerous
authorities from the analysis of pure cow’s milk:–

————–+——-+——+——-+—–+——+——+——–+——
Authority or |Number | | Total | |Solids| | |
Analyst. | of |Water.|solids.|Fat. | not |Sugar.|Caseine.|Salts.
| cows. | | | | fat. | | |
————–+——-+——+——-+—–+——+——+——–+——
| | p.c. | p.c. | p.c.| p.c. | p.c. | p.c. | p.c.
James Bell | 216 |87·17 | 12·83 | 3·83| 9·00 | .. | .. | 0·71
| | | | | | | |
James Bell | 24 |86·78 | 13·22 | 4·12| 9·10 | .. | .. | 0·72
|dairies| | | | | | |
| | | | | | | |
C. Estecourt | 22 |87·26 | 12·74 | 3·37| 9·37 | .. | .. | ..
|dairies| | | | | | |
| | | | | | | |
J. Carter Bell| 183 |86·40 | 13·60 | 3·70| 9·90 | .. | .. | 0·76
J. Cameron | 42 |86·53 | 13·47 | 4·00| 9·47 | .. | .. | ..
C. Cameron | 40 |87·00 | 13·00 | 4·00| 9·00 | 4·28 | 4·10 | 0·62
C. Cameron | 100 |86·75 | 13·85 | 4·60| 9·25 | .. | .. | ..
| | | | | | | |
Fleischmann } | 120 |87·78 | 12·22 | 3·20| 9·02 | .. | .. | ..
and Veith } | | | | | | | |
| | | | | | | |
Veith | 60 |87·20 | 12·80 | 3·10| 9·70 | .. | .. | ..
Veith | 9120 |86·97 | 13·03 | 3·52| 9·51 | .. | .. | ..
Wanklyn |Average|87·50 | 12·50 | 3·20| 9·30 | .. | .. | ..
| | | | | | | |
A. Wynter } | „ |86·87 | 13·13 | 3·50| 9·63 | .. | .. | ..
Blyth } | | | | | | | |
| | | | | | | |
Marchand | „ |87·15 | 12·85 | 3·55| 9·30 | .. | .. | ..
| | | | | | | |
Henry and } | „ |87·02 | 12·98 | 3·13| 9·85 | 4·77 | 4·48 | 0·60
Chevalier } | | | | | | | |
| | | | | | | |
Vernois } | „ |86·40 | 13·60 | 3·60|10·00 | .. | .. | ..
Becquerel } | | | | | | | |
| | | | | | | |
Payen | „ |86·60 | 13·40 | 3·50| 9·90 | .. | .. | ..
O. C. Wiggin | 58 |85·92 | 14·08 | 4·01|10·07 | 4·29 | 4·99 | 0·79
E. Calder | 27 |87·23 | 12·77 | 3·32| 9·45 | .. | .. | ..
Sharpless | 34 |85·85 | 14·15 | 4·62| 9·53 | 4·82 | 4·06 | 0·65
Haidlen |Average|87·30 | 12·70 | 3·00| 9·70 | .. | .. | ..
Letherby | „ |86·00 | 14·00 | 3·90|10·10 | 5·20 | 4·10 | 0·80
J. König | „ |87·30 | 12·70 | 3·00| 9·70 | 5·00 | 4·00 | 0·70
Boussingault | „ |87·40 | 12·60 | 4·10| 8·50 | 5·10 | 3·20 | 0·70
Muspratt | „ |86·43 | 13·57 | 4·43| 9·14 | 4·73 | 3·74 | 0·67
Dieulafait | „ |87·64 | 12·36 | 3·11| 9·25 | 4·22 | 4·18 | 0·85
Gorup-Bezanez | „ |85·70 | 14·30 | 4·31| 9·99 | 4·04 | 5·40 | 0·55
Brinton | „ |86·00 | 14·00 | 4·50| 9·50 | 3·50 | 5·50 | 0·70
| | | | | | | |
Chandler | 1700 |87·45 | 12·55 | 3·83| 8·72 | .. | .. | ..
| qts. | | | | | | |
| | | | | | | |
Newton |Average|87·50 | 12·50 | 3·50| 9·00 | .. | .. | ..
Bartley | „ |87·50 | 12·50 | 3·50| 9·00 | .. | .. | ..
White | „ |87·50 | 12·50 | 3·50| 9·00 | .. | .. | ..
Waller | „ |87·50 | 12·50 | 3·20| 9·30 | .. | .. | ..
Babcock | „ |85·53 | 14·47 | 5·09| 9·39 | 5·15 | 3·57 | 0·67
Church | „ |86·30 | 13·70 | 3·70|10·00 | 5·10 | 4·10 | 0·80
Edward Smith | „ |86·40 | 13·60 | 3·61| 9·90 | 3·80 | 5·52 | 0·66
Martin | „ |86·50 | 12·50 | 3·20| 9·30 | .. | .. | 0·67
————–+——-+——+——-+—–+——+——+——–+——

Mr. Martin obtained the following results from the examination of
cream separated by centrifugal force, and of skimmed milk:–

———–+———-+————-
| Cream. |Skimmed Milk.
———–+———-+————-
| per cent.| per cent.
Water | 52·21 | 90·34
Fat | 41·16 | 0·15
Sugar | 3·11 | 3·98
Caseine | 3·40 | 4·80
Salts | 0·12 | 0·78
———–+———-+————-

The proportion of mineral constituents in milk usually ranges between
0·7 and 0·8 per cent. The average composition of milk ash is as
follows:[20]–

Per cent.
Potassa 24·5
Soda 11·0
Lime 22·5
Magnesia 2·6
Ferric oxide 0·3
Phosphoric anhydride 26·0
Sulphuric anhydride 1·0
Chlorine 15·6
—–
103·5[21]

The tabulation below gives the composition of human milk and the milk
of various animals:–

————+——–+——+——-+——+——–+——-+———
|Specific|Water.| Milk | Fat. |Caseine.| Milk |Inorganic
|Gravity.| |Solids.| | |Sugar. | Salts.
————+——–+——+——-+——+——–+——-+———
| | p.c. | p.c. | p.c.| p.c. | p.c. | p.c.
White woman | 1·0315 |87·806|12·194 | 4·021| 3·523 | 4·265 | 0·28
Coloured | | | | | | |
woman | .. |86·34 |13·66 | 4·03 | 3·32 | 5·71 | 0·61
Mare | 1·0310 |91·310| 9·690 | 1·055| 1·953 | 6·285 | 0·397
Goat | 1·0323 |86·36 |13·64 | 4·36 | 4·70 | 4·00 | 0·62
Ewe | 1·0380 |82·94 |17·00 | 6·97 | 5·40 | 3·63 | 0·97
Sow | 1·0440 |81·80 |18·20 | 6·00 | 5·30 | 6·07 | 0·83
Canine | 1·0360 |77·26 |22·74 |10·64 | 9·21 | 2·49 | 0·44
Ass | 1·0330 |91·95 | 8·05 | 0·11 | 1·82 | 6·08 | 0·34
Camel | |86·94 |13·06 | 2·90 | 3·67 | 5·78 | 0·66
| | | | | \ | / |
Hippopotamus| .. |90·43 | 9·57 | 4·51 | 4·40 | 0·11
Elephant | .. |66·697|33·303 |22·070| 3·212 | 7·392 | 0·629
Porpoise | .. |41·11 |58·89 |45·80 | 11·19 | 1·33 | 0·57
Cat | .. |81·62 |18·38 | 3·33 | 9·55 | 4·91 | 0·58
Llama | .. |89·55 |10·45 | 3·15 | 0·90 | 5·60 | 0·80
————+——–+——+——-+——+——–+——-+———

Several varieties of preserved and condensed milk have, for a number of
years, been placed upon the market. The composition of the best-known
brands of these preparations is as follows:–

PRESERVED MILK.

———————-+———+———+———+———+——
| | |Cane and | |
Brand. | Water. | Fat. | Milk |Caseine. |Salts.
| | | Sugar. | |
———————-+———+———+———+———+——
| p.c. | p.c. | p.c. | p.c. | p.c.
Alderney | 30·05 | 10·08 | 46·01 | 12·04 | 1·82
Anglo-Swiss (American)| 29·46 | 8·11 | 50·41 | 10·22 | 1·80
„ „ (English)| 27·80 | 8·24 | 51·07 | 10·80 | 2·09
„ „ (Swiss) | 25·51 | 8·51 | 53·27 | 10·71 | 2·00
Eagle | 27·30 | 6·60 | 44·47 | 10·77 | 1·86
Crown | 29·44 | 9·27 | 49·26 | 10·11 | 1·92
———————-+———+———+———+———+——

CONDENSED MILK.

——————-+———+———+———+———+———
| | |Cane and | |
Brand. | Water. | Fat. | Milk |Caseine. | Salts.
| | | Sugar. | |
——————-+———+———+———+———+———
|per cent.|per cent.|per cent.|per cent.|per cent.
American | 52·07 | 15·06 | 16·97 | 14·26 | 2·80
New York | 56·71 | 14·13 | 13·98 | 13·18 | 2·00
Granulated Milk Co.| 55·43 | 13·16 | 14·84 | 14·04 | 2·53
Eagle | 56·01 | 14·02 | 14·06 | 13·90 | 2·01
——————-+———+———+———+———+———

ANALYSIS.

The principal adulterations of milk (watering and skimming), are
detected by taking its specific gravity, and making quantitative
determinations of the total milk solids, the fat, and the milk solids
not fat. Of these criteria, the last-mentioned is the most constant and
reliable.

_Physical Examination._

_a. Specific Gravity._–The instrument employed by the New York health
inspectors for testing milk is a variety of the hydrometer, termed
the lactometer, and its use, which is based upon the fact that under
ordinary conditions watered milk possesses a decreased density, is
certainly of great value as a preliminary test. The Board of Health
lactometer indicates specific gravities between 1·000 (the density of
water) and 1·0348. On its scale 100° represents the specific gravity of
1·029 (taken as the minimum density of genuine milk), and 0 represents
the density of water; the graduations are extended to 120°, equivalent
to a specific gravity of 1·0348. In taking an observation with the
lactometer, the standard temperature of 15° should be obtained,
_and the colour and consistency of the milk noted_. If these latter
properties indicate a dilution of the sample, and the instrument sinks
below the 100° mark, it is safe to assume that the milk has been
watered. The scale is so constructed that the extent of the dilution
is directly shown by the reading, _e. g._ if the lactometer sinks to
70° the sample contains 70 per cent. of pure milk and 30 per cent.
of water. As the standard of specific gravity (1·029) selected for
the 100° mark of the lactometer is the _minimum_ density of unwatered
milk, it is evident that the readings of the instrument will almost
invariably indicate an addition of water less than has actually taken
place. It would therefore appear that, under normal circumstances,
the standard adopted by the New York Board of Health errs on the side
of too much leniency toward the milk dealer. Cream being lighter than
water, a sample of skimmed milk will possess a greater specific gravity
than the pure article, and it is possible to add from 10 to 20 per
cent. of water to it and still have the resulting admixture stand at
100° when tested by the lactometer. Vehement attempts have been made in
court and elsewhere to impeach the accuracy of the indications afforded
by the lactometer. These have been mainly founded upon the fact that
a sample of milk unusually rich in cream will have a lower density
than a poorer grade, so that it is quite possible that milk of very
superior quality may show a gravity identical with that of a watered
specimen. Great stress has been laid upon this by the opponents of the
measures to control milk adulteration adopted by the public sanitary
authorities. They have contended that a chemical analysis should be
made. Recourse to this method would, however, involve a greater amount
of time than it is usually practicable to devote to the examination
of the numerous samples daily inspected; moreover, the process is
resorted to whenever the indications of the lactometer leave the
inspector in doubt. With the exercise of ordinary intelligence this
contingency seldom arises, as the proportion of cream required to
reduce the specific gravity to that of a watered sample would be more
than sufficient to obviate any danger of mistaking the cause of the
decreased density. In this connection it should be stated, that the
average lactometric standing of about 20,000 samples of milk, examined
by the New York State Dairy Commissioner in the year 1884, was 110°,
equivalent to a specific gravity of 1·0319.

The following table shows the value of lactometer degrees in specific
gravity:–

VALUE OF LACTOMETER DEGREES IN SPECIFIC GRAVITY.

———–+———–
Lactometer.| Gravity.
———–+———–
0 | 1·00000
1 | 1·00029
2 | 1·00058
3 | 1·00087
4 | 1·00116
5 | 1·00145
6 | 1·00174
7 | 1·00203
8 | 1·00232
9 | 1·00261
10 | 1·00290
11 | 1·00319
12 | 1·00348
13 | 1·00377
14 | 1·00406
15 | 1·00435
16 | 1·00464
17 | 1·00493
18 | 1·00522
19 | 1·00551
20 | 1·00580
21 | 1·00609
22 | 1·00638
23 | 1·00667
24 | 1·00696
25 | 1·00725
26 | 1·00754
27 | 1·00783
28 | 1·00812
29 | 1·00841
30 | 1·00870
31 | 1·00899
32 | 1·00928
33 | 1·00957
34 | 1·00986
35 | 1·01015
36 | 1·01044
37 | 1·01073
38 | 1·01102
39 | 1·01131
40 | 1·01160
41 | 1·01189
42 | 1·01210
43 | 1·01247
44 | 1·01276
45 | 1·01305
46 | 1·01334
47 | 1·01363
48 | 1·01392
49 | 1·01421
50 | 1·01450
51 | 1·01479
52 | 1·01508
53 | 1·01537
54 | 1·01566
55 | 1·01595
56 | 1·01624
57 | 1·01653
58 | 1·01682
59 | 1·01711
60 | 1·01740
61 | 1·01769
62 | 1·01798
63 | 1·01827
64 | 1·01856
65 | 1·01885
66 | 1·01914
67 | 1·01943
68 | 1·01972
69 | 1·02001
70 | 1·02030
71 | 1·02059
72 | 1·02088
73 | 1·02117
74 | 1·02146
75 | 1·02175
76 | 1·02204
77 | 1·02233
78 | 1·02262
79 | 1·02291
80 | 1·02320
81 | 1·02349
82 | 1·02378
83 | 1·02407
84 | 1·02436
85 | 1·02465
86 | 1·02494
87 | 1·02523
88 | 1·02552
89 | 1·02581
90 | 1·02619
91 | 1·02639
92 | 1·02668
93 | 1·02697
94 | 1·02726
95 | 1·02755
96 | 1·02784
97 | 1·02813
98 | 1·02842
99 | 1·02871
100 | 1·02900
101 | 1·02929
102 | 1·02958
103 | 1·02987
104 | 1·03016
105 | 1·03045
106 | 1·03074
107 | 1·03103
108 | 1·03132
109 | 1·03161
110 | 1·03190
111 | 1·03219
112 | 1·03248
113 | 1·03277
114 | 1·03306
115 | 1·03335
116 | 1·03364
117 | 1·03393
118 | 1·03422
119 | 1·03451
120 | 1·03480
———–+———-

_Chemical Examination._

_b. Water, Total Solids, and Ash._–Five grammes of the fresh milk are
weighed in a tared platinum dish, having a flat bottom, which is placed
on a water-bath, where it is allowed to remain for about three hours.
It is then transferred to a water-oven, and the dish is subsequently
weighed, from time to time, until the weight becomes constant. The loss
in weight is the _water_ present; the difference between the weight
of the platinum capsule and its weight with the remaining contents
gives the amount of _total solids_, which, in milk of good quality,
should not be under 12 per cent. The inorganic salts (ash) can now
be determined by carefully incinerating the residual contents of the
capsule. Too high a temperature is to be avoided in this process, in
order to prevent the fusion of the ash, which should, however, be
ignited until it shows a greyish-white colour. The amount of ash in
genuine milk ranges from 0·70 to 0·80 per cent. The addition of water
naturally decreases this proportion as well as that of the total
milk-solids.

_c. Fat, Milk Solids not Fat, Caseine, and Milk Sugar._–An approximate
estimation of the fat in milk was formerly made by the use of the
_creamometer_. This instrument consists simply of a long glass tube,
provided at its upper end with a scale. The milk under examination is
introduced into the tube and allowed to remain at rest for about 24
hours, or until the stratum of cream has completely collected upon
its surface; the quantity is then read off by means of the attached
scale. The results afforded by the creamometer are, however, far
from reliable. Cream is really milk rich in fat, caseine, etc., and
the quantitative relation it bears to the true amount of fat present
is not always a direct one. A recent form of _lactoscope_, devised
by Feser, is less objectionable, and is in very general use for the
rapid estimation of fat in milk. It consists essentially of a glass
cylinder, provided with two scales, one being graduated into c.c., the
other, into percentages of fat. In the lower end of the instrument is
a contraction, in which is placed a cylindrical piece of white glass,
graduated with well-defined black lines. In using the lactoscope, 4
c.c. of the milk are introduced into the instrument by means of a
pipette, and water is gradually added, with shaking, until the black
marks on the small white cylinder become just visible. Upon now
referring to the c.c. scale, the quantity of water used to effect the
necessary dilution is ascertained, and the corresponding percentage of
fat in the sample is indicated by the percentage scale.[22]

In the gravimetric determination of the fat (butter), 10 grammes of the
milk are put into a tared platinum dish, containing a weighed amount of
dry sand. The milk is evaporated as previously directed, the mixture
being constantly stirred with a small platinum spatula. The residue
is repeatedly treated with warm ether or petroleum naphtha of 70° B.,
and the solutions poured upon a small filter. The several filtrates are
collected in a tared beaker, and cautiously evaporated, until constant
weight is obtained. This will give the amount of _fat_. The undissolved
residue remaining in the platinum capsule, or the difference between
the quantity of fat and that of the total milk-solids, affords the
proportion of _milk solids not fat_ contained, which, in unadulterated
milk, should amount to 9 per cent. It has been determined by
experiment, that every percentage of milk-solids not fat, increases
the specific gravity of milk 0·00375, whereas each percentage of fat
decreases the gravity 0·0010, and the proportion of solids not fat can
be calculated from the data afforded by the lactometer and Feser’s
lactoscope by means of the formula:–

(S – A) / 0·00375,

where S is the specific gravity of the milk, as shown by the
lactometer, and A is the remainder obtained upon multiplying the
percentage of fat indicated by the lactoscope by 0·001 and subtracting
the residue from 1·0000.

The residue remaining after the extraction of the fat is treated with
warm water containing a few drops of acetic acid, or with dilute (80
per cent.) alcohol, in order to remove the sugar. The residue is
dried until it ceases to decrease in weight, and is then weighed. The
difference between the original weight of the sand and the weight of
the sand and residue combined represents approximately the amount of
_caseine_ (albuminoids) present. As this contains a certain proportion
of ash it is to be subsequently ignited, and the ash obtained deducted
from the first weight. The alcoholic sugar solution is evaporated to
dryness and weighed. The residue is then incinerated and the weight
of ash is subtracted. The difference is the amount of _milk sugar_
contained. The sugar may likewise be determined by means of Fehling’s
solution (see pp. 37, 111). About 50 c.c. of the milk is warmed with
a small quantity of acetic acid to precipitate the caseine, which is
removed by filtration, and the filtrate diluted to 500 c.c.; the test
is then applied. 10 c.c. of the copper solution represents 0·067 gramme
of milk sugar.

The sugar in milk can also be estimated by the polariscope (see under
Sugar, p. 112). In case the Ventzke-Scheibler instrument is used, 65·36
grammes of the sample are weighed out and introduced into a 100 cc.
flask; about 5 cc. of plumbic basic acetate solution is added, and the
liquid is well shaken, and then allowed to stand at rest for a few
minutes. It is next filtered, its volume made up to the 100 cc. mark,
and the 20 cm. tube filled and the reading made; this divided by 2
gives the percentage of sugar in the milk.

Mr. A. Adams[23] has recently proposed a method of milk analysis which
consists in first placing 5 cc. of the sample in a tared beaker, and
then introducing a weighed paper coil made of blotting paper from
which all fatty matter has previously been removed by washing with
ether. As soon as the milk is completely absorbed, the paper coil is
removed and dried at 100°. The increase of weight gives the amount of
_total solids_. The _fat_ is next extracted by petroleum naphtha or
ether, and its weight determined. The proportion of _solids not fat_ is
ascertained by again drying and weighing the exhausted coil.

The standards adopted by the English Society of Public Analysts for
pure milk, are:–

Per cent.
Specific gravity 1·030
Ash 0·70
Solids not fat 9·00
Fat 2·50
Total solids 11·50
Water 88·50

In the State of New York, the legal standards for milk are that it
shall not contain more than 88 per cent. of water, nor less than 12 per
cent. of milk solids, and 3 per cent. of fat.

In Massachusetts the law fixing a chemical standard of purity for milk
reads: “In all cases of prosecution, if the milk shall be shown upon
analysis to contain more than 87 per cent. of water, or to contain less
than 13 per cent. of milk solids, it shall be deemed, for the purpose
of this Act, to be adulterated.”

The Board of Health of New Jersey fixes the minimum amount of total
solids at 12 per cent. and the maximum amount of water at 88 per cent.
In Paris, the minimum limits _for condemnation_ are the following:–

Fat, 2·70; milk-sugar, 4·50; caseine, albumen, and ash, 4·30; total
solids, 11·50.

The following proportion can be employed in the calculation of the
amount of pure milk (_x_) contained in a suspected sample:–

From the total solids:–

12·5: total solids found = 100 : _x_.

From the solids not fat:–

9·30: solids not fat = 100 : _x_.

From the sugar:–

4·40: sugar found = 100 : _x_.

From the specific gravity:–

1·030 : sp. gr. = 100 : _x_.

In most cases the determination of the total milk-solids and the fat
(the difference being the solids not fat) furnishes all the data
required for determining the amount of watering which a sample of milk
has undergone. The Society of Public Analysts use 9 as the average
percentage of solids not fat in pure milk (which is generally
considered as too low) and adopt the formula:–

100/9 S = _x_,

in which _x_ represents the percentage of genuine milk, and S the
solids not fat.

PLATE IV.

[Illustration: Cream × 420.]

[Illustration: Cows Milk × 420.]

ARTOTYPE. E. BIERSTADT, N. Y.

In skimmed milk the percentage of fat removed (_x_) can be ascertained
by the formula:–

(2·5) / (9·0) S – _f_ = _x_,

in which S = solids not fat, and _f_ = the fat found. In case the
sample has been subjected to both skimming and watering, the water
added (_x_) can be calculated from the formula[24]:–

100 – (100 + 2·5) / 9 S – _f_ = _x_.

The addition of mineral salts to milk is detected by the increased
proportion of ash found; the presence of an abnormal amount of common
salt by the high proportion of chlorine present in the ash, which
in pure milk should never exceed 0·14 per cent. The use of sodium
bicarbonate, borax, etc., is also detected by the analysis of the
ash. Glycerine, salicylic acid, flour, and starch, if added, can be
extracted from the milk-solids and their identity established by the
usual characteristic reactions.

The microscope is of great service in the determination of the quality
of milk, and especially in the detection of the presence of abnormal
bodies, such as pus, colostrum cells, and blood. In pure cow’s milk the
globules are in constant motion; their usual size is 1/5000 of an inch,
but this depends upon the nature of the food used. Plates IV. and V.,
which represent cream, pure milk, skimmed milk, and milk containing
colostrum cells, were taken from photo-micrographic negatives furnished
through the kindness of Mr. Martin.

Numerous cases of severe illness have from time to time been developed
by the use of milk which was apparently free from any of the usual
adulterants. In a recent issue of the ‘Philadelphia Medical News’
(Sept. 1886) an instance of wholesale milk poisoning at Long Branch is
described, and the results reached by a careful study of the epidemic
are given. It was demonstrated that warm milk, fresh from the cow, if
placed in closed cans under conditions which retarded the dissipation
of its heat, may suffer fermentation resulting within a few hours in
the genesis of a sufficient quantity of a poisonous ptomaine (termed
_tyrotoxicon_) to produce dangerous toxic effects in those drinking it.

Tyrotoxicon was isolated from the milk, and obtained in needle-shaped
crystals, which reduced iodic acid and gave a blue coloration when
treated with potassium ferricyanide or ferric chloride. Prof. Victor
C. Vaughan[25] discovered the same alkaloid in poisonous cheese, and
has also detected its presence in ice-cream that had been the cause
of sickness. In this connection it is of importance to note that
the addition of gelatine to ice-cream is occasionally practised:
in case this substance is used while in a state of incipient
decomposition, the danger of the bacteria and other organisms present
subsequently resuming activity is considerable. It has been repeatedly
and conclusively demonstrated that milk from cows affected with
tuberculosis and other complaints, is capable of propagating the seeds
of disease, especially in children. The presence of impure water in
milk constitutes another source of danger. A test based upon the fact
that water which has received sewage contamination often contains
nitrites, is applied by first coagulating the suspected milk with
acetic acid, then filtering and adding to the filtrate a few cc. of an
equal mixture of sulphanilic acid and naphthylamine sulphate, when, in
presence of nitrites, a rose-red colour will be produced.