AND ITS MEMBRANES IN THE HORSE. 
593 
the arachnoid becoming* inflamed, while we concede without 
scruple this power to the pleura and the peritoneum. Do not the 
same phenomena occur in inflammation of the arachnoid as in 
that of other serous membranes ] Do we not daily witness in 
the horse the pleura itself quite healthy, although its surface 
is clothed with adventitious membrane, and its sub-serous tissue 
is thickened and injected] I must confess I cannot understand 
the difference drawn between these phlegmasia^. 
However, I feel myself in justice bound to add, that inflamma¬ 
tion of the spinal arachnoid is by no means common, and that it 
is a membrane that rarely manifests the organic alterations so 
frequently observable in analogous tissues. In point of fact, 1 
have never remarked fibrous chords issuing from its surface; and 
among the divers examinations I have made of horses with palsy 
of the hind extremities, I have not once met with the fibrinous 
depositions so commonly seen upon the exhaling surface of in¬ 
flamed pleurae: nevertheless, the adventitious fibrous membrane 
observed by M. Dupuy in a paralysed ox, and the observations 
and experiments made by M. Renault on the cerebral arachnoid 
of the horse, leave no doubt that such morbid productions may 
form, in certain cases, as well upon the spinal arachnoid as upon 
other serous membranes. 
In the sound state, the spinal sheath always contains a little 
limpid serocity, the product of the perspiration continually oozing 
from the surface of the arachnoid. This serocity, in phlegmasiae 
of the spinal membranes, becomes more or less coloured, and 
sometimes augmented in quantity. We must take care never 
to confound this with the cephalo-spinal liquid inclosed within 
the lamellae of the pia mater. 
- When we are desirous to test the coloration and quantity of 
the liquid contained in the sheath, it is of great importance that 
we calculate the time elapsed since death; for the longer that 
interval, the more considerable the quantity. It would appear 
also, that, at a certain period (about two days after death), the 
colouring matter of the blood transudes through its vessels and 
through the arachnoid, and tinctures this fluid, reddening it 
more or less, which has long been erroneously regarded as a 
pathological condition; so that it is not until all this has been 
taken into the account, that we are authorised in setting down 
as a pathological phenomenon either the quantity or the tinge of 
this serous fluid. 
Inflammation of the pia mater is a more frequent occurrence 
in the horse : it is almost always accompanied by some sensible 
alteration in the spinal marrow, though sometimes it exists alone. 
In either case, the principal phenomena of this inflammation 
