In the interpretation of the Lotman-Picken photograph of muscle it would be helpful
to be able to estimate with confidence the relative quantities of the materials responsible
for the α-keratin portion and the crystalline portion of the observed x-ray scattering.
As a possible practical approach to this problem I have prepared a photograph of a
horsehair to which are attached three very fine, needle-like crystals of urea. The
urea crystals were so long that they extended beyond the x-ray beam in both directions
along the fiber. Since the density of urea (1.335) is close to that of the density
expected for horsehair (about 1.3), the relative amounts of urea and horsehair in
the beam could be taken as proportional to their respective cross sections. These
respective cross sections, as calculated from measurements of the hair and the crystals
with a micrometer eyepiece, were found to be in the following ratio:
cross section of crystals = 0.0029 mm.2 = 0.05
cross section of hair 0.06 mm.2
[Data Equation]
Maximum error of measurement, 10%
The attached photograph was made by rotating the combined sample in a beam of copper
radiation; sample to film distance, approximately 3.25 cm. A flat-film Unicam camera
was used.
It is interesting, although perhaps not significant, to note that Bloor ("Biochemistry
of the Fatty Acids", p.200) lists the following data on the composition of dry muscle
tissue.
[Data Table]
John E.
