2 
are of various sizes and ages, together with 
eggs. 
By examination with the microscope, this 
mite will be 8een to have a globular body with 
eight legs, both body and legs being covered 
with scattered hairs. The legs, with the excep- 
tion of two, have a hook and sucker attached 
to each, and those two have a long hair-like 
appendage. 
The insect is called by Gerlach Dermatodectes 
ovis — literally, skin-biter of the sheep. He 
computes the rate of increase as follows : — 
1st generation in fifteen days, 10 females and 5 
males 
6th generation in ninety days, one and a-half 
millions 
The small amount of injury these minute 
creatures can produce by their bites will not 
account for the great torment the sheep en- 
dures, so that we must infer from the results 
that a poisonous- fluid, secreted by the insect, 
is at the same time introduced into the wound, 
and that the poison is the chief cause of the 
irritation, 
We see similar effects from the bites of mos- 
quitoes, sand-flies, and ticks ; the wounds 
made by these creatures being altogether insig- 
nificant. 
Their powers of endurance after removal 
from the living sheep is believed to be great. 
On examining skins of sheep killed a fortnight, 
I have found all the insects dead. From what 
is known on this subject it is quite clear that 
the scab insect cannot be propagated except 
from eggs, and, if the creatures were once com- 
pletely destroyed from Australia, they could 
not again come into existence without impor- 
tation. 
Many contagious diseases have a spontaneous 
origin, or what appears to be spontaneous to 
our present knowledge, hut, in the case of scab, 
the fact holds good, omne vivum ex ovo. 
Many applications have been used to destroy 
the scab insects, amongst which are various 
compounds of mercury and arsenic. 
Mercurial ointment was much used in Eng- 
land, and frequently produced salivation and 
death of the animals. 
Corrosive sublimate dissolved in water, to 
the extent of an ounce to the gallon, is not so 
liable to produce salivation, but is still a dan- 
gerous compound. 
Such washes are liable to drip upon the 
grass, which thereby becomes poisonous to the 
fiheep, great numbers having thereby perished. 
After using su.h solutions it is advisable to 
keep the sheep in a yard until the fleeces dry. 
Arsenic is the active ingredient in most of the 
washes sold, and is combined with various 
substances of a less noxious quality. 
Six ounces of arsenic, with an equal weight 
of carbonate of potash, added to fourteen gal- 
lons of water, is highly recommended. 
The caustic soda now imported in iron cases 
for the soap makers, would be cheaper and 
better than the potass. 
Tobacco has properties which recommend it 
as the safest wash for general purposes, and, 
being free from the deleterious qualities of 
mercury and arsenic, should be used by all in- 
experienced men. 
Half a pound of the coarse rank tobacco, 
which can be grown here so plentifully, is 
sufficient for a gallon. It should not be 
boiled in the water, but have boiling water 
poured on it. Boiling expells some of its 
active principles. ‘Half-an ounce of caustic soda 
per gallon adds much to it efficacy. If more 
tobacco could be used it would be advisable. 
Sulphur is the great remedy for itch in the 
human subject, and is more potent if combined 
with potass or soda. By heating six pounds 
of caustic soda with one of sulphur for a short 
time over a fire, the sulphur amalgamates with 
the soda and becomes soluble in water. 
This article will be found very effective in 
eradicating scab, half-an-ounce of which to the 
gallon makes a wash that is not poisonous to 
the sheep. Tobacco mixed therewith forms 
the wa h, in my opinion, the best that can be 
used. 
In employing this wash, it will be most con- 
venient, to construct a wooden tank four fiet 
deep, into which the sheep can be driven a few 
at a time. An inclined plane, constructed on 
the Bide the sheep get out, allows the wash 
that drips from the wool to run again into the 
tank. If arsenic be used the efficacy of that 
mineral can be increased by the addition of 
the caustic soda. 
It is important to hear in mind that the eggs 
of the scab insect are killed with greater 
difficulty than the insect itself. This is the 
cause of the continuance of the disorder. To 
eradicate the pest, the sheep should he dipped 
in an effective solution weekly, for the space of 
a month, and if there be any suspicion of the 
continuance of the affection, dipping ought to 
be used until all suspicion is removed. In 
using tanks of wash the labour of dipping is so 
much diminished that the prolonged attention 
necessary is not found very inconvenient. 
Printed at the “Guardian Office,” Brisbane. 
