stripped from those portions which are to be examined microscopically. To remove the pia an incision is made on the median surface of each hemisphere just above the corpus callosum from one extremity to the other, and the pia stripped back first from the median and then from the convex surface. The stripping is done by means of the fingers, with occasional aid from the forceps.

Section of the Brain.-There are several methods of cutting up the brain, no one of which is particularly suitable to all occasions. That method must be chosen which is most fitted to the individual case and to the use to which the tissue is to be put.

The ideal method from a neuro-pathological standpoint would undoubtedly be to harden the brain entire, and then to make serial frontal sections thin enough for microscopical purposes through the whole organ. The nearest approach to this ideal method is to harden the brain entire in formaldehyde, a process occupying ten days to two weeks (see page 303), to make thin serial sections, to mordant the sections, divided if necessary into smaller pieces, in a chrome salt (preferably by Weigert's quick method), and then to carry through a number of series from the important parts for microscopical examination. By this means the relations of the various cerebral structures and of the pathological lesions can be perfectly preserved and studied. This method can be particularly recommended for tracing degenerations in the motor tract.

If there is a noticeable focal lesion, such as a tumor or hemorrhage, it should be so incised, generally frontally or horizontally, as best to show its relations to the important cerebral tracts and ganglia. In these cases also the best results are obtained by hardening the brain entire in formaldehyde, and later making serial sections for macroscopic study or for carrying through for histological purposes. In many cases, however, it is necessary or advisable to examine the lesions in the fresh state. For instance, if it be desired to study the neuroglia-fibers, it is positively necessary to cut out thin slices of fresh tissue and to fix them immediately in

the proper solution. Often, too, the lesion cannot be or is not found except on fresh examination, or the clinician whose case it is desires to see at once the cause of certain symptoms. Under such circumstances the more ideal method must be sacrificed, and as much made out of the case as is possible in the condition in which it is left after the examination.

For the routine examination of the brain, to demonstrate

FIG. 9.-First cut in the brain (Nauwerck).

its topography and to bring to light suspected or unsuspected lesions, probably no method is more generally used than Virchow's. The objection most often made against it is that the cerebral cortex is too much cut up. In case, however, it is desired to preserve the cortex or parts of it for microscopic purposes, the longitudinal incisions after the first may be omitted, and the cortical portion, after being separated from the stem, may be cut in any way that seems advisable. In like manner, the brain-stem or any other part

may be left uncut, and hardened entire in formaldehyde for histological purposes.

Virchow's Method. The brain is to be placed on its base in the same position as one's own. Press the hemispheres apart a little so as to expose the corpus callosum. Hold the left half of the cerebrum in the left hand with the fingers on the lateral aspect and the thumb in the longitudinal fissure. Then make an almost vertical incision with a long, slender knife through the roof of the left ventricle in its middle third, 2 to 3 mm. from the median raphé of the corpus callosum. The roof of the ventricle is to be slightly raised vertically by the thumb, so that the incision, which must not be too deep, may not injure the basal ganglia. The incision is to be continued into the anterior and posterior cornua. Then make a long incision from one end of the above cut to the other, passing just outside of the basal ganglia at an angle of about 45°. Repeat the process on the right side, turning the brain half around. Next seize what remains of the corpus callosum and fornix in the middle, lift them, and cut through from below up, passing the knife through the foramen of Munroe. The parts are then turned back, exposing the velum interpositum and the choroid plexuses. By drawing back the velum interpositum the third ventricle is uncovered.

The corpora quadrigemina are exposed by cutting transversely the right posterior pillar of the fornix and adjoining brain-substance and carrying them over to the left. Each ventricle as it is opened is to be carefully inspected and any abnormal condition of its ependyma noted. The cortex is further divided on one side, and then on the other, by holding it in the left hand and making vertical straight sections from the upper angle of the previous cut into the convex cortex, allowing the sections to fall apart, so as to avoid touching and soiling the surface with knife or fingers. Each portion thus cut represents a prism. The incisions should go well into the cortex, but not so far as to separate the different pieces. The basal ganglia are examined by means of a number of frontal sections. For this purpose the left hand is placed palm upward underneath the brain, so that as

each section is made over the tips of the fingers by one long stroke of the knife it falls forward, exposing a clean surface of which the two halves can be compared. An incision is next carried through the middle of the pineal gland, the corpora quadrigemina, and the vermiform process of the cerebellum, opening the aqueduct of Sylvius and the fourth ventricle.

Each half of the cerebellum is divided by a median hori

zontal section into halves, and these portions are still further subdivided by a series of cuts radiating from the peduncles.

In order to make sections of the pons and medulla the brain is folded together and turned over. Several crosssections are then made with the left hand placed beneath as in sectioning the basal ganglia.

Before making the sections it is well to remove the basilar and vertebral arteries, especially if they are calcified.

In Pitre's method of dissecting the brain the lateral ventricles are opened as in Virchow's method. Then the pedunculi cerebri are cut squarely across, so as to remove the pons

and cerebellum, and a longitudinal incision is carried down through the third ventricle, halving the cerebrum. Through each half of the cerebrum a series of six sections is then made parallel to the fissure of Rolando. The names of the sections and the important parts which they show are as follows:

1. The pre-frontal section through the frontal lobe, 5 cm. anterior to the fissure of Rolando, shows the gray and white substance of the frontal convolutions.

2. The pediculo-frontal section through the posterior portions of the three frontal convolutions shows the anterior extremity of the island of Reil, the lenticular and caudate nuclei, and the internal capsule.

3. The frontal section through the ascending frontal convolution, parallel to the fissure of Rolando, shows the optic thalamus, the lenticular and caudate nuclei, the claustrum, the external and internal capsules, the anterior portion of the descending horn of the lateral ventricle, and the island of Reil.

4. The parietal section through the ascending parietal convolution shows portions of the same structures as the preceding, and a transverse view of the hippocampus.

5. The pediculo-parietal section through the parietal lobe, 3 cm. posterior to the fissure of Rolando, shows the tail of the caudate nucleus in two places and the posterior portion of the optic thalamus.

6. The occipital section through the occipital lobe, I cm. in front of the parieto-occipital sulcus, shows simply the white and gray matter of the occipital lobe. The cerebellum, pons, and medulla are incised in the manner already described.

Removal of the Spinal Cord.-The body is to be placed face downward, with the head over the end of the table and a block under the chest. The incision is made over the spinous processes from the occiput to the sacrum. Dissect the skin and muscles back on each side, so as to leave the vertebral laminæ as bare as possible. The laminæ may be cut through by means of several instruments, of