In the anatomical, physiological, and pathological conditions referred to above we find to a certain extent an explanation of the action of what the Germans, especially the mechano-therapeutists, call assistive and resistive treatment.

As our most important instrument in assistive as well as in resistive treatment we have the will, and it is only because we have daily evidence of this before our eyes that we often fail to give it its full value in hygiene as well as in therapeutics.

It is by active voluntary movements that in our earliest periods of life we begin to exercise our will, and we continue also throughout life to exercise it in this way, when the opportunities for its exercise are manifold.

It cannot be doubted that voluntary movements play a specially important part in the whole psychological development of the child. It is obvious that voluntary movements not only exercise the will of a young child, but are also valuable in developing his power of connecting cause and effect, his ideas of dimension, distance, time, etc., which facts, although not directly connected with medical gymnastics, are too interesting not to be mentioned here.

Another very important fact, Which concerns medical gymnastics rather more, but also involves considerable intellectual, ethical and practical consequences, is that voluntary movements exercise a special kind of thoughtful and at the same time active attention.

By attention to our movements, especially those of the upper extremity, besides the educative gain of various kinds, we increase "dexterity" which is of great value for many different occupations. for artists and surgeons no less than for actual labourers and mechanics. Dexterity requires a clear consciousness of intention, well worked out in every detail, for each movement, the absence of all pathological disturbing influences (tremor, etc.), and a specially fine co-ordination which momentarily conveys to each muscle taking part in the movement exactly the amount of innervation most suited to attain the object of the movement.

It is a necessary part of my present task to emphasise the fact that in all such finely co-ordinated, precise movements both the synergist and antagonist muscles taking part are undoubtedly innervated.

How the innervation of the synergist muscles and their antagonists behaves from a physiological standpoint cannot yet be said to be decided. H. E. Hering, Mann, and Sherrington are agreed that at the same time as we send impulses to those muscles causing movement we send also inhibitory impulses to their antagonists. In the opinion of many observers, however, this occurs to very different degrees, and O. Kohnstamm states that the ability of the practised workman to perform greater external work than the unpractised workman depends upon the former's unconscious exercise and skill in completely doing away with tone and innervation in the antagonists. Sherrington explained quite recently that in his experiments on apes in regard to flexion of the elbow joint he had never seen simultaneous contraction of the extensors. It is, however, certain, as has been noticed by many investigators, that increased contraction of the antagonists of muscles performing certain movements takes place under certain conditions due to increased innervation. In slow, carefully calculated movements one can clearly feel the firmness of the antagonists taking part, and we have good reason to suppose that innervation of these also takes place in every movement requiring specially careful co-ordination.

The influence of the will upon the activity of the neurons has only lately become more clear to human consciousness. Hypnotism and suggestion have shown how the will of others is able to control various kinds of sensibility, cause sudden amaurosis in a quite normal eye, produce anaesthesia in the most hyperaesthetic, hysterical patient, etc. We see also that strong-minded drunkards are able by means of a firm resolve and subsequent auto-suggestion to change both the smell and taste of their favourite drink from being pleasant to being repulsive to themselves. The will may stand in the same relation to the motor neurons. By will and the consequently increased muscle innervation we are able, when necessary, to increase suddenly the strength of our movements to an enormous degree, far over our usual ability; by will and the exercise of it in connection with movements we are able, as Exner expresses himself, to assist and open up movement neurons, and by will we can also resist and repress both certain reflexes and other expressions of sensibility.

In the assistive and resistive treatment there are also other means, partly mechanical, partly quite outside mechano-therapeutics.

E.g., it is possible to control the spasm of a choreic child by applying plaster bandages over the greater part of its body, and experienced physicians are to be found who consider this the most effectual of the innumerable means used in the treatment of chorea.

There are other "internal" means. The attacks of cramp in strychnine poisoning may be controlled by large doses of chloral, which diminishes irritability, or by small doses of curare, which, without entirely paralysing, reduces strongly the activity of the muscle nerve-end plates. We can control the motor storms of the hysterical patient by administering bromide. We exercise an "assisting" effect upon the nerves by the electric current, constant or interrupted. We have also in strychnine an effectual "internal" means of "assisting" by raising irritability. But as soon as any impulse from the will reaches the muscles we have, both in the motor voluntary impulses and in the movements, as good a means of "assisting" as any other.

Assistive exercise treatment consists chiefly of gymnastics which we make use of to regain entire conductive power in the nerve paths where it has been more or less rendered difficult, i.e., specifically in pareses.