s, the "Coagulometer." In certain conditions, particularly in
acute exanthemata, and in the various forms of the haemorrhagic
diathesis, the clotting time is distinctly increased, or indeed clotting
may remain in abeyance. Occasionally a distinct acceleration in the
clotting, compared with the normal, may be observed. Wright has further
ascertained in his excellent researches, that the clotting time can be
influenced by drugs: calcium chloride, carbonic acid raise, citric acid,
alcohol and increased respiration diminish the clotting power of the
blood.

Recently Hayem has repeatedly called attention to a condition, that is
probably closely connected with the coagulability of the blood. Although
coagulation has set in, the separation of the SERUM FROM THE CLOT occurs
only very slightly or not at all. Hayem asserts, that he has found such
blood in Purpura haemorrhagica, Anaemia perniciosa protopathica, malarial
cachexia: and some infectious diseases.

For such observations large amounts of blood are needed, which are
clinically not frequently available. Certain precautions must be
observed, as has been ascertained in the preparation of diphtheria
serum, so that the yield of serum may be the largest possible. Amongst
these that the blood should be received in longish vessels, which must
be especially carefully cleaned, and free from all traces of fat. If the
blood-clot does not spontaneously retract it must be freed from the side
of the glass with a flat instrument like a paper-knife without injuring
it. If no clot occurs in the cold, a result may perhaps follow at blood
temperature.

In spite however of all artifices and all care, it is here and there,
under pathological conditions, impossible to obtain even a trace of
serum from considerable amounts of blood. In a horse for example which
was immunised against diphtheria, and had before yielded an unusually
large quantity of serum, Ehrlich was able to obtain from 22 kg. of blood
scarcely 100 cc. serum, when the animal was bled on account of a tetanus
infection.

Perhaps a larger _role_ is to be allotted in the diseases of the blood
to these conditions. Hayem already turns the incomplete production of
serum to account, for distinguishing protopathic pernicious anaemia from
other severe anaemic conditions. A bad prognosis too may be made when for
example in cachetic states this phenomenon is to be observed.

A few methods still remain to be mentioned which test THE RES