casionally both are available for examination. During the
desiccation in the air, generally complete in 10-30 seconds, the
preparations must naturally be protected from any dampness (for example
the breath of the patient).

The extent of surface which is covered depends on the size of the drop,
the smaller the latter, the smaller the surface over which it has to be
spread. Large drops are quite useless, for with them, the one
cover-glass swims on the other, instead of adhering to it.

Although a written description of these manipulations makes the method
seem rather intricate, yet but little practice is required to obtain an
easy and sure mastery over it. We have felt compelled to describe the
method minutely, since preparations so often come under our notice
which, although made by scientific men, who pursue haematological
investigations, are only to be described as technically completely
inadequate.

The specimens so obtained, after they are completely dried in the air,
should be kept between layers of filter-paper in well closed vessels
till further treatment. In important cases, preparations of which it is
desirable to keep for some considerable time, some of the specimens
should be kept from atmospheric influences by covering them with a
layer of paraffin. The paraffin must be removed by toluol before
proceeding further. The preparations must naturally be kept in the dark.

[beta]. Fixation of the dry specimen.

All methods of staining available for the blood require the fixing of
the proteids of the blood. A general formula cannot be given, since the
intensity of the fixation must be regulated in accordance with the kind
of stain that is chosen. Relatively slight degrees of hardening suffice
for staining in simple watery solutions, for example, in the triacid
fluid, and can be attained by a short, and not too intense action of
several reagents. For other methods, in which solutions that are
strongly acid or alkaline are employed, it is however necessary to fix
the structure much more strongly. But here, too, an excess as well as an
insufficiency must be guarded against. It is easy with the few staining
fluids that are in use to ascertain the optimum for each.

The following means of fixation are employed.

1. Dry Heat.

A simple plate of copper on a stand is used, under one end of which
burns a Bunsen flame. After some time a certain constancy in the
temperature of the plate is reached, the part neare