286 FLUIDITY AND PLASTICITY
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from two-thirds to three-quarters of the viscosity of the blood.
The fluidity of the blood of cold-blooded animals is higher than
that of warm-blooded animals, but the rabbit is peculiar among
warm-blooded animals in having blood of exceptionally high
fluidity.
1 Milk.—The fluidity of the milk of a cow differs from day to
[ day as well as with different individuals and at different periods
| of life. The fluidity of woman's milk is highest directly after
! childbirth and falls off nearly 50 per cent during the period of
nursing. The milk of goats is less fluid than that of cows.
According to Cavazzani (1905) the addition to milk of small
amounts of NaOH or KOH produces a change in the fluidity of
ri the milk of a cow, goat, or horse but does not affect the fluidity of
P woman's milk. According to Alexander1 human milk contains
[ a protective colloid not present in cow's milk, hence coarse curds
^ are not formed on adding acids.
I The action of ferments upon milk has been studied by Gutzeit
u (1895) and Fuld (1902). The decline in the viscosity of a solu-
I tion of proteins during digestion by means of trypsin has been
the subject of study by Spriggs (1902). The greater part of the
loss in viscosity occurs considerably before the completion of
!• the digestion, according to Bayliss (1904). This is in accordance
i with the idea that the destruction of the structure must lower the
viscosity tremendously, whereas the splitting of microscopic
\ particles may increase the viscosity and the splitting of amicro-
| scopic particles decreases the viscosity. Spriggs (1902) and
1 Zanda (1911) investigated the changes in viscosity during diges-
I tion by pepsin.
) Ceramics and Glass Making.—The thorough mixing of glass
t melts, the removal of bubbles of gases, and the pressure necessary
! to blow the glass at a given temperature all depend upon the
i fluidity of the melt, hence the control of the fluidity of glass
t melts is of importance.
1 j The Seger cone method of determining temperatures suggests
f the possibility of measuring high temperatures by the viscometric
method. Barus proposed to use the viscosity of a gas for this
purpose.
The manufacture of porcelain is concerned with the principles
1J. Soc. Chem. Ind. 28, 280 (1909).