emaly, Microscepi’'| On the Real Nature of Disease Germs. 193 
times below the median line of the valve, and varies greatly in its 
relative size. It appears to have reference to the nuchal furrow of 
Beyrichia, Primitia, and Leperditia. Kirkbya having relationships 
with Beyrichia, Primitia, Moorea, and Leperditia, is one of the 
Leperditiade.* To Leperditia it is related through Beyrichia 
and Piimitia. In general form, hingement, ventral overlap, and 
even sometimes in a faint bilobation of the surface, the valves of 
Kirkbya resemble those of Beyrichia; but the double and some- 
times threefold ventral rims, and especially the subcentral pit and 
the longitudinal riblets, distinguish them. ‘The ventral ridges, to 
some extent, and the pit have their analogues in Primitia ; but this 
genus generally presents convex forms ; and when flattish its valves, 
though sunken (as in P. excavata), have no costation. Moorea 
presents flattish valves, marginally ridged, but without any sub- 
central pit or dorsal furrow. 
The oldest known Kirkbya is K. fibula of the Ludlow division 
of the Silurian rocks. No other has yet been found in this geolo- 
gical system, nor any in the Devonian rocks ; but some Carboniferous 
strata at home and abroad abound with individuals belonging to one 
or other of ten species ; and at least one form, with six varieties or 
very closely allied species, is plentiful in the Permian limestones of 
Europe and Britain. 
6. Moorea is a Paleozoic Bivalved Entomostracan (previously 
referred to) with compressed valves, smooth or punctate, bounded 
more or less completely by a raised marginal ridge as in some 
Kirkbyz, but not marked by any trace of a dorsal sulcus or sub- 
central pit. The Upper Silurian strata have yielded one (Fig. 16), 
and the Carboniferous Limestone two species of this genus. 
III.—On the Real Nature of Disease Germs. By Lionsn §. 
Beare, F.R.S., Fellow of the Royal College of Physicians, and 
Physician to King’s College Hospital. 
Berore I proceed to describe the characters of the particles sus- 
pended in animal fluids, having virulent contagious properties, it is 
very desirable to draw attention to the minute particles of bioplasm, 
which may be demonstrated in many specimens of simple exudation. 
From this subject we shall pass on to the consideration of other 
forms of “exudation” which possess specific disease-producing 
properties. We shall find that by a careful microscopical exami- 
nation of fluids which experience has proved to us have contagious 
properties, facts of great interest are disclosed which have an 
* See ‘Ann. Nat. Hist.,’ ser. 2, vol. xvii., p. 99, 
+ Ibid., ser. 4, vol. iii., p. 224, pl. 15, fig. 9. 
