358 
distinguished would be ggdyth or ygdyth of 
a line square, and thus they would be much 
larger than those of whose existence a very 
simple process of reasoning is sufficient to con- 
vince us. 
BIBLIOGRAPHY.—The following works may be 
referred to.— Hooke, Micrographia, Lond. 1665. 
Baker, Of Microscopes, Lond, 1785 Adams, On 
the Microscope, Lond. 1787. Brewster, Treatise 
on the Microscope from Encyclopedia Britannica, 
also Treatise on new Philosophical Instruments. 
On Optics, Lardner’s Cyclopedia. Lister, in Phil, 
Trans, 1829. Chevalier, Des Microscopes, Par. 
1839, Mandl, Traité Pratique du Microscope, Par, 
1839. Pritchard and Goring, Micrographia ; also, 
by the same authors, Microscopic Illustrations and 
Micadacopie Cabinet. Slack, Holland, and Turrell, 
in Trans, Soc. Arts, vol. 49. Penny Cyclop. art. 
Microscope, Hildebrandt, Anatomie, Band. i. p. 128. 
( W. B. Carpenter.) 
MILK.—(Taaa, Gr.; lac, Lat.; le lait, 
Fr.; die Milch, Germ.; latte, Ital.) The 
secretion of the mammary gland. In treating 
of the milk it will perhaps be best, previous to 
entering upon its description as produced by 
the human subject, to give a general account 
of the secretion as obtained from the cow, such 
being the most familiar example afforded to us. 
Milk may be regarded as a serous fluid, hold- 
ing in suspension minute white globules com- 
ig of casein and fatty matter. These glo- 
ules have been microscopically examined by 
Raspail, who states them to have a diameter 
of .00039 inch, and to disappear on the 
addition of a solution of potassa. The most 
recent microscopic observations on the milk are 
those of Professor Nasse, of Marburg,* who 
gives the following as the constituents of the 
normal secretion of the mammary gland :—Ist, 
smooth, homogeneous, transparent oil globules 
and large oil globules, also the common milk 
globules; 2d, cream globules, distinguishable 
by their facette-like appearance; 3d, granu- 
lated yellow corpuscles; 4th, the lamelle of 
epithelium; 5th, the more or less turbid 
medium in which the four preceding kinds of 
a are suspended. 
he common milk globules are composed of 
fatty matter, which dissolves rapidly in ether. 
No membrane can be seen investing them. The 
first nine days after delivery the largest globules 
measure x};th of a line in diameter, but subse- 
quently become as large as y}gth, but they vary 
in size throughout lactation. The cream glo- 
bules are considered by Professor Nasse to be 
formed after the milk has been drawn or 
exposed to the air, for in fresh woman’s milk 
no globules but the common milk globules 
above described are discernible: the cream 
globules occur as large as Ath of a line in dia- 
meter. The yellow granulated corpuscles are 
culiar to the colostrum; their diameter is 
M q}oth to sisth of a line; some are found mea- 
suring Zsth of a line in length and jth in breadth. 
They are composed of fatty matter. The author 
considers them analogous to the mucus cells 
cast off from mucous membranes, and thinks 
that perhaps they come from the gland ducts. 
From my own observations I am inclined to 
* Miiller’s Archiv, 1840, Heft iii. p. 258. 
MILK. 
think that the cream globule of Nasse exists 
even in fresh milk, and may easily be seen in 
specimens containing but little fatty matter. I 
lately saw them in the milk of a woman who 
had suckled for seven months. I have not 
been able to rid the milk of globules by ether 
or liq. potasse. If milk be agitated with ether, 
then allowed to stand, and the lower stratum 
of fluid examined, we can detect distinct 
globules in it—globules of all sizes, and 
the appearance described by Nasse as i 
to the cream globule. From the variety in size 
which I have so constantly observed, I cannot 
understand how any author can have made 
his mind to give an admeasurement to the 
globule of milk; for my own part, after much 
careful observation, I feel convinced that the 
milk contains nothing which deserves the name 
of a true organic globule. That globules exist 
I do not deny, and these I believe to be what 
have been described by Nasse as cream ar 
bules, appearing when milk has creamed, 
cause the adhering fatty matter is separated ; 
but, notwithstanding, being very obvious before 
creaming occurs, in specimens of fresh milk 
containing a small proportion of fatty matter. 
The serum in which these particles float 
composed of water, holding in solution 
alkaline lactate and chloride with traces 
sulphate and phosphate, lactates of lime and 
magnesia, sugar of milk, and animal extractive. 
Oxide of iron and an earthy phosphate are to 
be detected in the ashes of milk, but these, in 
all probability, are derived from the casein of 
the secretion. When milk is allowed to remain 
at rest for some hours, a pellicle forms on its 
surface, varying with the nature of the milk: 
this is what is called the cream, and consists of 
the fatty or butyraceous matter of the milk in 
combination with a varying proportion of casein. 
It is from this tebe i butter is obtained by 
churning, by which operation the bu 
particles unite into a mass to the exclusion of 
the casein, which remains suspended in the 
serum, and thus forms a mixture known y the 
name of butter-milk or lait de beurre of the 
French. The whole of the casein, however, 
cannot be removed from the butter 
its minute particles being entangled 
cohering fatty globules, and it is in 
measure Owing to its presence that butter is 
more or less prone to me rancid and de- 
composed. Milk from which the cream has 
been removed still retains the greater of 
the casein, and when this is precipi from 
it by the action of rennet, we obtain a curd, 
which, being pressed and dried, constitutes 
cheese. The clear liquor se from this 
curd contains the more soluble matters of milk, — 
viz. the alkaline salts with the sugar of pre | 
and in Switzerland a considerable quantity of 
this sugar is manufactured from whey and used 
for household purposes. I have it it 
best to notice the various operations in domestic 
is 
an 
of 
ee ~ 
2S ae 
economy to which the milk is subjected, not 
only because by them several of its proximate 
elements are eliminated, but likewise that the 
reader may have some familiar object with — 
which to connect the following account of the 
