likewise erroneous and easily leads to absurdity. Onesided destruction of the cerebral hemispheres in man produces no forced movements. Thus, according to Steiner, the cerebral hemispheres should not belong to the brain. Second, according to Steiner,

the ear must be a brain. One-sided lesion of the ear is sure to produce forced movements in a series of animals, and, moreover, the auditory nerve is a higher sensory nerve. I have mentioned this subject at this place because it is a typical illustration of what plays on words in physiology lead to. It is not our task to find a definition for the word brain, but to gain an insight into the functions of the central nervous system. It is of minor importance what name we give to the different parts of the central nervous system.

In connection with this chapter we wish to call attention to the more recent experiments of Sherrington and H. E. Hering, from which it seems to follow that with the innervation of a muscle the relaxation of its antagonist results simultaneously.

BIBLIOGRAPHY.

1. LOEB, J. Ueber Geotropismus bei Thieren. Pflüger's Archiv, Bd. xlix., 1891.

2. LOEB, J. Ueber den Antheil des Hörnerven an den nach Gehirnverletzung auftretenden Zwangsbewegungen, Zwangslagen und associirten Stellungsänderungen der Bulbi und Extremitäten. Pflüger's Archiv, Bd. 1., 1891.

3. STEINER. Die Functionen des Centralnervensystems und ihre Phylogenese. II. Die Fische. Braunschweig, 1888.

4. BETHE, A.

Vergleichende Untersuchungen über die Functionen des Centralnervensystems der Arthropoden. Pflüger's Achiv, Bd. lxviii., 1897.

5. BETHE, A. Das Centralnervensystem von Carcinus mænas. II. Mittheil. Arch. f. mikroskop. Anatomie, Bd. 1., 1897.

6. STEINER, J. Die Functionen des Centralnervensystems wirbelloser Thiere. Sitzungsberichte der Berliner Akademie der Wissenschaften. 1890, I. S., 39.

CHAPTER XI

RELATIONS BETWEEN THE ORIENTATION AND FUNCTION OF CERTAIN ELEMENTS OF THE SEGMENTAL GANGLIA

The results of some investigations carried on by Garrey and myself showed that if a constant current be sent through a trough in which are larvæ of Amblystoma, peculiar changes may be observed in the postures of the animals (1). If the current passes through them longitudinally from head to tail (Fig. 37) the back becomes convex and the ventral side

FIG. 37. ATtitude of an AMBLYSTOMA UNDER THE INFLUENCE OF A GALVANIC CURRENT PASSING FROM HEAD TO TAIL.

+

FIG. 38. ATtitude of an AMBLYSTOMA WHEN THE GALVANIC CURRENT PASSES FROM TAIL TO HEAD.

concave. This change of position is occasioned by the muscles of the ventral side (the flexors of the spinal column) becoming more tense than the dorsal

muscles (the extensors of the spinal column) from the passage of the current. On the other hand, if the current goes through the animal in the direction from tail to head both head (Fig. 38), and tail are raised. The body becomes more concave on the dorsal side and convex on the ventral side. The extensors of the spinal column become more tense than the ventral muscles. A pronounced opisthotonus exists. In order to show the phenomenon clearly the animal must be brought into the current gradually. If we continue to raise the intensity of the current, changes of position also take place in the legs. The changes in the hind-legs are more easily described than those in the fore-legs. If the current passes from head to tail the hind-legs are braced backward (Fig. 37), making the forward movement (to the anode) easier. If the current passes from tail to head the hind-legs are braced forward (Fig. 38), making the backward movement (to the anode) easier. How can these phenomena be explained? The current has two kinds of effects. A conduction of the current takes place through ions. Wherever the progress of ions is blocked in the central nervous system, an increase in their concentration will occur and this must be followed by physical or chemical alterations of the colloids. The progress of ions may be blocked by semipermeable membranes at the external limit of neurons or somewhere inside the neurons. Wherever anions are blocked different effects (anelectrotonus) will be produced than at places where the progress of kations is

blocked (katelectrotonus). The action of the various ions on nerve-elements is as yet unknown. The other effect of the current may consist in the migration of certain colloids in one direction and of water in the other direction.

If in the larvæ of Amblystoma the tension of the flexors of the spinal column predominates in a descending current (from head to tail) and the tension of the extensors of the spinal column predominates in an ascending current, this proves that the nervous elements of the flexors and extensors in the central nervous system, which are affected by the ions, possess an opposite orientation. Maxwell and I have developed more definite ideas concerning the orientation of these elements, but such details are for the time being of minor importance. I only wish to state that the relative orientation of these elements must be the same in every segment of the spinal cord; for when the spinal cord in the larvæ of Amblystoma is severed or the whole animal cut into several pieces the effects of the current remain the same. Since the article mentioned above was published I have found that crayfish (young and small specimens were used for these experiments) behave toward the current like Amblystoma larvæ. If the median-plane of the crayfish is in the direction of the lines of the current (which are all straight and parallel in these experiments) and the head is turned toward the anode, the flexors of the body contract and the crayfish rolls itself into a complete ring, provided that the density of