602 MEANS OF DETERMINING THE QUALITY OF MILK. 
meter, or specific-gravity test; 3d, the lactoscope of M. 
Donne; and 4th, the microscope. It may be necessary to 
make a few remarks on the use of these several instruments, 
and first, of the lactometer. A glass tube, of about eleven 
inches long, and half an inch in diameter, is filled with milk 
to within a short distance of the top, the surface of the 
fluid being made to coincide with a transverse line drawn 
on the tube, and marked zero ; the capacity of the tube 
from this line downwards is divided into one hundred equal 
parts or degrees. When the tube thus filled has been suf¬ 
fered to remain undisturbed for a definite time, say twelve 
hours, or twenty-four hours, the quantity of cream which 
shall have separated spontaneously during that time is ascer¬ 
tained b} r an inspection of the instrument held in a proper 
light, as the inferior limit of the stratum of cream is gene¬ 
rally defined with sufficient clearness to enable one to read 
off accurately the per-centage of this ingredient which has 
become separated from the milk within the time specified. 
In using this instrument, it is necessary to observe certain 
precautions: the milk should be quite fresh, but the tube 
should not be filled till the milk has cooled down to the 
temperature of the place where it is destined to remain while 
at rest; the entire mass of milk should always be well 
stirred up immediately before the sample to be tested is 
taken out; the lactometer, when filled, should be left undis¬ 
turbed for about twelve hours if the weather be warm, for 
twenty-four hours if it be cold. Milk which has been thus 
tested is said to show a certain per-centage of cream, and the 
higher the number of degrees indicated by the lower edge of 
the cream-stratum, the more of this ingredient is the milk 
supposed to possess. As far as this goes, nothing can be 
more simple and satisfactory, if it were only true; but it can 
be shown that the indications of the instrument in question 
are fallacious, and calculated to lead to the most erroneous 
conclusions, especially in the case of those milks in regard 
to which it is most important that the information supplied 
by this test should be as accurate as possible—for example, 
in those cases in which milk is supplied by contract in large 
quantities to public institutions. The fact is unquestionable 
that contractors are in the habit of supplying a liquor which 
they call milk, at a price so excessively low that they must 
either add a large proportion of water, or sustain a serious 
loss ; and the managers of large institutions are often satisfied 
to accept this so-called milk at the price agreed upon, pro¬ 
vided the lactometer shows a certain per-centage of cream. 
In reference to the effect which the addition of water to milk 
