306 D. J. HAMILTON. 
Other grave sources of error are undoubtedly post-mortem 
change and the method of preparing specimens for examina- 
tion. Ihave very often found that all manner of lesions, soften- 
ings, areas of disintegration, varicose nerve-sheaths, &c., can 
be artificially produced by merely placing the specimens, 
while they are being hardened, in an atmosphere with a 
temperature such as is generally maintained in our ordinary 
households. One of the most important conditions for drawing 
correct conclusions is, especially for the first week, to keep 
the temperature of the parts to be hardened as low as possible 
—at 32° F. or very slightly above it. In this way we can 
prevent decomposition until the reagent used in hardening 
has had time to penetrate into the interior of the tissue, and 
partially to harden it by a process very similar to what is 
pursued in tanning. 
If, again, we place the part in too strong a solution of 
chromic acid, the outer limits become so rapidly hardened as 
effectually to prevent the ingress of reagents to the interior, 
which accordingly undergoes decomposition. My own 
method of preparation, described further on, is calculated to 
do away with these deficiencies, and to present the specimens 
to the eye as nearly identical with the appearances during 
life as possible. 
The experiments which are about to be described were 
undertaken with the object of first producing a lesion which 
we know to be an inflammatory one, and then making the 
most careful examination, all preconceived ideas on the sub- 
ject of inflammation generally being purposely laid aside. 
The appearances were merely carefully noted and abundantly 
verified by repetition of the experiments and observations. 
Everything is purposely omitted which could mislead, for 
want of confirmation, and only those facts which by constant 
repetition were found to be invariable are here stated. I have 
also been favoured with the valuable confirmatory evidence 
of Professor Stricker, in whose laboratory for experimental 
pathology the observations were made. 
Method of experimenting.—A small animal, such as a cat, 
having been narcotized, the spinal cord is eut down upon in 
the upper lumbar region, at the junction of the dorsal and 
lumbar portions. A thread is passed through it for about an 
inch in a longitudinal direction. The ends of the thread 
are then tied, the wound stitched up, and the animal left for 
forty-eight hours. This gives abundant time for the excite- 
ment of inflammation. ‘The animal is then killed and the 
spinal cord cut out. 
Preparation of the cord. —The dura mater having been 
