284

FLUIDITY AND PLASTICITY

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Metallurgy.—The terms hardness, ductility, pliability, mallea-
bility are terms which are probably, like the term plasticity,
complex in character and may in time come to be more precisely
defined in terms of friction and mobility. It is desirable to
know the friction and mobility of each modification of each
metal and their several alloys, and also the effect upon these
properties of changes in crystal size or shape and in the amount
of amorphous solid between the crystals. This subject merits
extended treatment. We know that annealing gives the crystals
opportunity to develop whereas cold working tends to break up
the crystal structure and thereby toughens the metal. Quench-
ing the hot metal of course prevents crystal growth and should
decrease the yield point. There is no doubt but that polishing
and similar operations result in a plastic flow of the surface layers
of a metal.
Biology, Medicine and Pharmacy.—It would be out of place
here to treat in detail of the very numerous papers which have
been devoted to biological subjects. Beginning with Poiseuille
who was first drawn to his study of fluidity through his interest
in the circulation of the blood in the capillaries, there has been a
continued interest in the viscosities of animal liquids. The
viscosity of the blood in various individuals and species of animals,
in various pathological conditions as well as under the influence
of anaesthetics and drugs, the effect on viscosity caused by differ-
ences in diet, age, sex, or temperature outside of the body, the
effect upon the viscosity of the blood produced by the removal of
certain organs of the body have all been subject to investigation.
The composite character of the blood has prompted inquiries in
regard to the viscosity of blood serum and defibrinated blood as
compared either with blood as it exists within the animal or as it
is freshly drawn. The other body fluids, milk, lymph, perspira-
tion, the vitreous humor, et cet., have all been studied and carefully
reviewed by Rossi (1906).
Rossi finds that preceding the coagulation of a solution there is
an increase in viscosity which is the best measure of the progress
toward coagulation. The more viscous the original solution, the
more rapidly does the formation of the gel proceed. Fano and
Rossi (1904) found that electrolytes always first cause a drop in
the viscosity which is then followed by a rise as the concentration