when the tissue is hardened in Müller's fluid. It is much better, on the whole, to put the greater part of the brain, spinal cord, nerves, and muscles into Müller's fluid after it has been hardened in formalin, and to harden some of the more important smaller pieces in absolute alcohol immediately after removal from the body. Such preparations can also be stained for bacteria.

It requires several months to harden a brain in Müller's fluid. The time can, however, be considerably shortened by keeping the jar in a temperature of about 30° C.

The solution must be constantly renewed; during the first six days, if the jar is kept in a warm place, the solution should be renewed every day, later at longer intervals. As the hardening process goes on additional incisions, either horizontal or frontal, should be made from time to time to allow the chrome salts to penetrate the tissue more easily. The tissues should never be examined until they are completely hardened; the pieces must be brown, not yellow. If the hardening is incomplete, unpleasant artifacts will be produced when the tissue is stained.

Hardening in absolute alcohol requires only a few days. The alcohol should be changed several times. After a tissue has been hardened in Müller's fluid it is to be cut in thin slices and hardened again in alcohol, but without dehydrating, if it is intended to use a medullary sheath stain. The tissue is then placed first in thin and then in thick celloidin for the purpose of imbedding. After an interval varying from five to twenty days, or even longer, depending on the size of the pieces, the tissues are mounted on blocks and laid in 70 per cent. alcohol; after a few hours they are ready to cut.

The cutting is done with a microtome, and the sections need not be very thin. If an uninterrupted series of sections is desired, a piece of firm medicated toilet-paper, which has been previously labeled, is moistened with a sugar solution, placed on a plate, and covered with a layer of thin celloidin. The sections are then laid in order on

the paper, to which they immediately adhere. This is kept in 70 per cent. alcohol. When the sections are to be examined, they are easily loosened from the paper by placing the latter in water. To stain the nerve-fiber, Weigert-Pal's hematoxylin stain for medullary sheaths is used. To stain the cells carmin or double carmin stain is used for tissues hardened in Müller's fluid, and Nissl's methylene-blue for tissues hardened in alcohol. (For further directions the student is referred to the textbooks of Kahldon, Friedländer-Eberth, and others.)

With the medullary sheath stain all the medullated nerve-fibers are stained black; hence if such fibers are normally absent, or if they are degenerated or destroyed, the corresponding areas are not stained and appear pale instead of black. The fatty constituents of the medullary sheath enter into a firm chemic union with the pigment of the hematoxylin, and this produces the black color.

The most modern method, Golgi's impregnation with silver (Cajal), can be used in pathologic cases only under certain restrictions, as it does not work uniformly well.

Our knowledge of the structure of the nervous system has been gained chiefly by means of the following methods of investigation:

1. By reconstruction of serial sections through a normal, fully developed human brain (Stilling, Meynert, etc.), various methods of staining or impregnation being used (Weigert, Golgi, Cajal, and Nissl).

2. By the examination of pathologic cases, especially of secondary degenerations (Türck, Waller).

3. By comparative anatomy and comparative embryology (Meynert, Edinger, and others).

4. By a study of the development (medullation, etc. Kölliker, Kupffer, His, Flechsig, and others).

5. By the examination of degenerations produced experimentally (Gudden, Monakow, and others).

These methods have been used as much as possible in the preparation of the plates contained in this

BIBLIOGRAPHY.

The following works, which have been utilized by the author in the preparation of this epitome, are recommended as admirable reference books for students of neurology:

1. Anatomy.

The text-books of Koelliker (Gewebelehre), Henle, HoffmannSchalbe, Raube, Gegenbaur. Monographs: von Flechsig (Leitungsbahnen, Plan des menschlichen Gehirns), Lenhossek (minute structure), Edinger (twelve lectures), v. Gehuchten (Gehirnanatomie), Bechterew (Leitungsbahnen), Obersteiner (Anleitung zum Studium der nervösen Organe). The works of Meynert, Gudden, His, Golgi, Cayal, and others.

2. Physiology and Pathology.

Charcot (lectures), Erb (Electrotherapie, Rückenmarkskrankheiten in 'Ziemssen's Handbuch," vol. XI), v. Strümpell (text-book), Leyden (clinical lectures), Wernicke (Gehirnkrankheiten), Gowers ("Diseases of the Nervous System "), Seeligmüller (text-book), P. Marie (lectures), Liebermeister (lectures), Eulenburg (article on "Nervous Diseases" in the Encyclopedia), Mendel (ibid., article on the "Brain"), Oppenheim (text-book), Hirt (text-book), Déjerine ("Centres Nerveux"). Leube (diagnosis); the works of Westphal, Kussmaul, Nothnagel, Munk, Hitzig, Lichtheim, Ferrier, and many others.