MICROSCOPIC DRAWING AND ENGRAVING. 
constitution. —87. Magnified view of a drop-of milk. —88. The butter 
globules.—89. Their number variable.—90. Analysis of the milk of 
different animals.—91. Richness of woman’s milk.—92. Analogy of 
milk to blood.—93. Importance of the quality of milk.—94. Its. 
richness ascertained.—95. Quevenne’s hydrometer applied to milk. 
—96. Its fallacy. — 97. Donne’s lactoscope. -—98. Objections to it 
answered.—99. Frauds practised by milk vendors.—100. Fore-milk 
and after-milk.—101. Self-engraved photographic pictures. 
64. Dk. BoNOino, having directed his researches to the itch 
insect, found that it was very nimble in its motions, covered with 
short hairs, and furnished with a formidable head, from which a 
pair of strong mandibles projected. 
■ At the extremities of its four pairs of legs, there are feet of 
remarkable form, each of which is provided with a sucker, by 
means of which he inferred that it sucks or draws its way under 
the skin, having first^xcavated a space for itself with its man¬ 
dibles. The insects form their nests there, deposit their eggs, and 
multiply rapidly. 
65. More recently, Dr. Bourguignon has studied the habits of 
this insect by means of a microscope specially adapted to the 
purpose, and has confirmed the discoveries of Bononio. He found 
that the insect fastens itself in the furrows of the skin by means 
of the suckers of its feet, aided by small bristles, being likewise 
covered with similar bristles in various parts of its body, by which 
it fixes itself more firmly, while it works its way with its man¬ 
dibles ; it is not furnished with eyes, but in a moment of danger 
it quickly draws in its head and feet, this motion and that of its 
gait resembling those of a tortoise. It usually lays sixteen eggs, 
which it deposits, ranged in pairs, in the furrows under the 
skin, where they are hatched in about ten days.* 
66. The insect which produces or accompanies the mange in 
horses, and which is called the acanis-exidcerans , is represented 
in fig. 37, p. 49, magnified in its linear dimensions one hundred 
and fifty times. 
67. This animalcule is larger and more easily obtained than 
the former; it is found under the whitish scales which are de¬ 
tached from the skin of the horse, and if several individuals be 
taken, they will be found to be in different states of development, 
having four pair of legs when full grown ; the two foremost pairs 
are terminated in a strong and sharp claw, and their general form 
is like that of the legs of a flea, consisting of five joints or 
segments. 
The head consists of nothing but a mouth, in which the organs, 
of mastication are seen, consisting of a pair of very fine and sharp 
* Bourguignon, quoted by “ Hoggon the Microscope, p. 318. 
98 
