What Bell called "the muscle-sense" is supplied really by sensory nerves from the skin, tendons, muscles, and joints. The nerves from the skin and their end bulbs indicate to us our various movements and positions by telling us of the tension in the different skin areas; the sensory nerves in the joint capsules act in a similar manner; the sensory nerves from the tendons seem to be specially important for our realisation of the resistance to our movements, and the nerves of the same kind in our muscles tell us the degree of their contraction. In these last cases the end apparatus of deeper sensibility consists of "Pacinian" bodies (or Vater's corpuscles), and of "Krause's end-bulbs" (not Meissner-Wagner's).

To a great extent our positions and movements are controlled by the small remarkable organs in the inner ear, in certain parts of the "labyrinth." We must especially note the "semi-circular canals" which seem necessary, for the maintenance of our power of equilibrium, and for the performance of at least part of our own movements with the head (Mach, Breuer). New research and opinions are exceedingly interesting concerning the otoliths in the utricle and saccule, otherwise filled with lymph, the sensory cilia found there and our dependence upon all these structures (even upon the lymph) in taking our bearings in regard to the position of the head and in movements of progression. It is possibly in the labyrinth also that we must look for an important, so to speak peripheral reflex organ for the tone of the whole skeletal musculature (Ewald), which tone, according to modern opinion, does not depend upon automatic nervous activity, but upon reflexes. For further details of these conditions, which are still far from having been fully thrashed out, I must refer the reader to the larger physiological text-books and to special works on this subject.

I have already shown that if the information from these organs of deeper sensibility and from widespread areas of skin is broken off or becomes incomplete, our movements suffer both in strength and certainty; that, e.g., if the posterior, sensory nerve roots of a dog are cut, symptoms arise which give an impression of true paralysis, in spite of the anterior motor roots being uninjured. In affections of the innermost parts of the ear spoken of above there arise giddiness and inability to maintain the erect position and to walk. In tabes dorsalis ( = syphilitic degeneration in the posterior sensory tracts of the spinal cord) arise the swaying, uncertain movements already spoken of, dependent upon disturbances of co-ordination which makes up ataxia.

To some extent the sense of sight helps us in these cases, and as long as we are able to see our movements and positions we arc better able to perform the former and to maintain the latter than when blindfold (Romberg's symptom = the inability of a tabetic patient to maintain the erect position with eyes shut).

The anomalies of the nervous system which come for mechano-therapeutic treatment, especially for medical gymnastics, differ widely in their character in regard to their pathological anatomy, clinical origin, and prognosis.

We treat by gymnastics both central and peripheral nervous diseases, e.g., both tabes dorsalis and (the results of) acute anterior poliomyelitis on the one hand, and traumatic or rheumatic neuritis on the other. The anatomical changes in these, as in many other cases, are well known; some cases however of nervous disease (e.g., hysteria) belong to the so-called functional neuroses, and we have no idea as to the underlying pathology.

The symptoms we desire to combat may be hypotonic or hypertonic. In the former we have abnormally weak innervation, as in pareses; in the latter innervation is too strong and causes tonic or clonic spasm (cramp). In other cases we find irregular innervation, as in the ataxy of tabes or in the tremors of occupation (co-ordination) neuroses.

All these phenomena may, especially in the functional cases, be found side by side. Hysteria may cause tonic blepharo-spasm or tonic muscular contracture in the elbow joint, or clonic spasm both in the sphincter of the eye and in the flexors of the arm; the patient sometimes has paralysis in these and other muscles, and is perhaps also much annoyed by tremor.

In other cases various symptoms belong to various stages. We have first hypertonic phenomena, when the nervous elements are subject in the beginning to severe irritation; by degrees and in proportion to the development of degenerative protoplasmic changes severe hypotonia and paresis arise.

How shall we explain the effects of medical gymnastics in these cases ?

To begin with we rely on the fact that the neurons depend for their nutritive condition on their activity; they suffer equally from too much as from too little work. If we prevent too strong and increase too weak activity of the neurons, it is to be supposed that we shall affect them therapeutically. We see then also that gymnastics, which exercises the neurons, has throughout much more influence upon hypotonic than upon hypertonic diseases; in the latter rest is generally the chief indication.

We also rely on our knowledge of the nutritive interdependence of the various parts of the neurons. If we are able to restore to normal disturbed nutrition in a ganglion cell, we know that in this way we undoubtedly also restore to normal similar disturbed conditions in the corresponding nerve fibres and end apparatus.

Finally, we support our claim to therapeutic effect in this direction on our knowledge of the fact that the nervous centres may be made to act vicariously for each other. We do not know how this takes place; it is probable that an increased knowledge of the functions of the dendrites and the characteristics of development will assist towards greater clearness in these matters. It is perhaps partly upon the development of this substituting power of the neurons that our obvious advance in raising the power of co-ordination in ataxia by means of active gymnastics depends.