J. F. SHIRLAW                                         299

In the majority of cases, P. gibsoni has never been detected in the blood
throughout the course of the illness, even in the terminal stages when profound
anaemic changes are present.

The post mortem picture is typical and easily summarised : changes mainly
affect the spleen and liver. In acute cases of a short duration of illness, the
spleen is markedly enlarged, increased up to ten times the normal weight, dark
red in colour or even chocolate, the follicles enlarged and prominent. In one
case, the spleen was grossly enlarged, filling the abdominal cavity, intensely
haemorrhagic in appearance and several haemorrhagic infarcts were promi-
nent. The spleen in these cases is softer in texture and somewhat diffluent.
In more protracted cases it is firmer in texture, somewhat ' fibroid ' occasion-
ally, with less prominent follicles. The liver is similarly grossly enlarged : in
one case, 16.6 per cent of the body weight. (The percentage weight of the
liver to the body weight in health is 3 per cent. Sisson.). The organ appears
finely cirrhotic, darker or slaty in colour, the surface granular and studded
with petechiae and frequently bile-stained.

The blood is thin and watery.

The systemic lymph glands are swollen and haemorrhagic.

The heart muscle usually shows an acute interstitial myocarditis.

The mucous membrane of the gastro-intestinal tract is covered with a
sticky mucuous deposit. Petechiae are frequently prominent and occasionally
discrete areas of ulceration. The duodenum in its first part is deeply stained
with bile and occasionally the pylorus.

In acute cases, the red bone marrow is hyperaemic and increased in amount
at the expense of the fatty marrow. In more chronic cases, this change is not
so evident.

Histopathological changes have been centred on the spleen, liver and
bone marrow.

                                             SPLEEN

The follicular lymphoidal cells are increased in number and mitosis is
evident, especially in peripheral cells where these seem to be undergoing a
transformation into larger cells (polyblast, transitional plasma cells, and
macrophages) with a clear cytoplasm and irregular nucleus—a type of cell
which is prominent in the red pulp. It is possible that these cells are in actua-
lity cells which have originated from the red pulp and are not derived from the
peripheral cells of the follicle, which they would then appear to infiltrate. The
inconspicuous and shrunken appearance of the follicles in chronic cases would
seem to support the idea and it appears probable that in an advancing infection
the red pulp of the spleen, actively mitotic as are its component cells, gradually
infiltrates and replaces the white pulp.

The most characteristic changes are in the red pulp. There is a very
definite hyperplasia of the cells of this tissue, with prominence of the cords of
Billroth. Coincident with the marked hyperplastic changes, degenerative