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INDIAN WOOL II. ASSESSMENT OF QUALITY [Vol. XXIII, Part II,
types of fibres in the sample. But though it may be convenient method of assess-
ment form the manufacturing point of view, it is not a correct measure of degree of
medullation since a single fibre may be partly medullated and partly unmedullated.
The extensive examination for ,the period of about nine years in this laboratory show
that the proportion of such partially medullated fibres is very large and hence to get
more realistic idea the method adopted in the laboratory has particular advantage
over other methods. This method of assessment of medullation has a special ad-
vantage from the point of view of breeding experiments over the method of assessing
the percentage of medullated fibres in a sample. It is felt that the method followed
by Mahal, Johnson and Burns of separating the fibre types is also not convenient
since it does not give a quantitative idea of medullation.
So far the methods available for the medullation assessment has been based on
the observation of Elphik. When wool fibres are immersed in a liquid like benzene
the refractive index of which is the same as that of wool, all the wool fibres become
invisible while hair stand out, dead white in appearance due to their hollow struc-.
ture and they can be easily picked out on account of their clear visibility. Although
an idea of the total degree of medullation in a sample may be obtained in this way,
its quantitative determination is rendered impossible on account of the presence of a
large number of partially medullated fibres which may have developed medullation
along the major portion of their lengths or may be medullated irregularly at intervals.
MacMahon [1937], however, claims to have the Elphick benzene method quan-
titative by employing a photoelectric cell to show the degree of medullation by the
amount of light reflected from the opaque white medullated fibres immersed in
benzene. The degree of medullation is thus given by the amount of galvanometer
deflection produced when a known weight of the wool sample in a blackened glass
tray is illuminated under a constant source of light. Hair reflects considerably more
light than pure wool when in benzene. An integration of the amount of light reflected
or the apparent whiteness of the sample would, therefore, give an index of the degree
of medullation. Based on this principle MacMahon used a photoelectric instrument
(medullometer) for the purpose. Though this method is quick for assessing medu-
llation, it has not been quite a success; as a number of factors have to be considered
which requires careful control such as the fluctuation in light intensity, the fatigue
shown by the photo-cell, the proper arrangement of the fibres and the refractive
index of benzene employed.
It was, therefore, found necessary for this reason, that a more direct, simpler and
at the same time more reliable method should be evolved which could be adopted for
use in the routine work of medullation assessment.
When the image of the wool fibre is projected on the screen for the measurement
of diameter, medullation appears along the length of the fibre as dark channels,
continuous or broken as previously noted. Therefore, while measuring the diameter
of the fibre, if the total length of the individual fibres and of medullated portion
in each of them is also measured, the percentage amount of medullation in the
total number of fibres measured could be easily calculated.
The results obtained by these two methods, viz. microprojection and medullo-
meter methods are shown in Table I.