158 METHODS OF ANALYSIS OF WOOL FIBRE [Vol. XXIV, Part III,
Estimation
The sample is allowed to condition in an electric oven at 102° F. for one day
and is then weighed accurately in the torsion balance (Plate VII, Fig. 2). It is then
spread on a velvet board to a length of six inches and three bunches of
approximately 200 fibres are drawn at random from the basal end. These are
conditioned in the oven and are weighed accurately in the torsion balance. The
number of fibres in each of the bunches is counted and the number of fibres in the
entire sample is calculated on the basis of weight and number of fibres in a bunch.
Since three bunches are drawn, average weight and count are taken of three bunches,
on the basis of which the total population of fibres in the entire sample is calculated.
It will be of interest to mention that a fine woolled sheep like the Merino has a
density of 20,392 fibres but the indigenous Deccani sheep carries only, 2,292 fibres
per 4 sq. cm. while the selected Deccani flocks carry 4,238 fibres per 4 sq. cm.
HAIRINESS OR MEDULLATION
The presence of hairiness is one of the main defects not only in the fleeces of
Deccani sheep but also in the majority of the breeds of sheep in India. Hairy
fibres can be distinguished from the non-hairy by the absence of the medullary
canal when the latter are viewed under the microscope. Hence, an evaluation of
this defect of hairiness is necessary for breeding sheep with an all wool coat.
Method
For quick method of distinguishing wool from hair, all that is required is a
black enamelled tray of 10 in. X 8½ in., a glass plate of 8 in. X 6 in. and benzene.
The test is carried out by placing a sample of wool which may contain hairy
fibres, in the tray. The sample is weighed down by the glass plate and benzene is
poured into the tray till the glass plate is immersed completely in benzene. Only
hair is visible and wool disappears apparently, as wool and benzene have the same
refractive index. This method is suitable as a field test, for rapid selection of non-
hairy sheep.
The method is rather slow and since no calculable values can be worked out, the
medullometer (Plate VIII, Fig. 1) evolved by McMahon is a very useful instrument
for the rapid assessment of medullation in wool sample. The principle is that a
hairy sample reflects light in benzene unlike the pure wool. The light reflected by
the hairy or partially hairy fibres is converted into an electric current. When this
current is passed through a mirror galvanometer, it gives reflection on a graduated
ruler corresponding to the light reflected by the sample.
Details of the apparatus
Four milky lamps each of 200 watts are connected in parallel through a volt-
meter of multirange 300/8/4 volts switch board type, and a rheostat of three amperes
current capacity and 100 ohms, is connected to the mains. Rheostat controls the
voltage and the intensity of light. The box which receives the reflected light is
fitted vertically at a distance of 5½ in. from the tray. It has two sliding boxes.
The lower box carried a cinepher condenser of four inches focal length and 5¼ inches
diameter while in the top one is fitted a photronic cell of high sensitivity (Weston