membered by you; it will be again brought before you in connection with the great chemico-vital process of the renewal of tissue, in its association with the origin of disease.

Nerves are of various thickness. At their origin they are thickest; and, like arterial blood-vessels, they become more and more minute in their ramifications, until they become too small to be seen with the naked eye. Their structure includes the most minute blood-vessels and absorbents necessary for the renewal of their component matter.

Such is the outline of the anatomy of nervous structure. There are many more minute particulars which anatomists describe as the result of their microscopic examination; but I have here mentioned what it most concerns you to understand, and which you must remember.

Whatever may be the real nature of nervous power, the nerves are its conductors from its various sources, which are called nervous centres or ganglia: these are central masses of a special structure, by which the nervous power is generated. They are the brain, the spinal cord, or spinal marrow, and the numerous minor nervous centres or ganglia, which are named according to their situation in the body, and the organs they supply.

Could I convey to you, dear Sir, a perfect knowledge of the nervous systems of the human body, could I enable you to view them in the minute anatomy and physiology of their nervous centres and of their nerves, could you understand all these in their different uses, connections, and dependences, as a whole, you could not fail devoutly to acknowledge that they are excellent in design and perfect in their adaptation. They are well declared, by those who have knowledge of them, to constitute the Divine masterpiece of animal mechanism. But I must refer you to larger works for a minute account of them; I can only give a general outline in this brief treatise.

Concerning these centres or sources of nervous power, let me, firstly, tell you of the cerebrum or brain. It is divided into two halves or hemispheres, and is the organ of the reasoning

faculties of man, and gives out the mandates by which the will calls the muscles into action.

At the base of the brain are placed the ganglia of the special senses, which become the instruments of instinctive actions in animals. In man they are the instruments of emotions, feelings, appetites, and passions, which are under the government of his reasoning faculties for their just regulation. Too often, alas! do they govern instead of being governed! Thus it is that intellectual man is so frequently found degraded in vice and misery, from which the lower animals are protected by their unerring instinct!

I must just mention to you that the cerebellum or little brain, which is placed below and behind the cerebrum, is the source or ganglion of animal power, and has also to do in the correct regulation of muscular action.

In strict anatomy and physiology, the spinal cord or spinal marrow must be considered as belonging more to the organic than to the animal nervous system, although it is frequently classed with the latter by medical authors, because of its being the medium by which volition and sensation are sent from the brain for voluntary muscular action, and other purposes of animal life. It is, in fact, a medium of connection between the

two systems of nerves. It is not what it was formerly supposed to be, a mere bundle of nerves continued from the brain. It is a distinct apparatus for supplying nervous power for muscular action, whether of voluntary or of involuntary kind. The former, or voluntary muscular action, in connection with sensation and volition, connects it with the animal system of nerves; the latter connects it with the organic system.

The spinal cord is the special ganglion or nervous centre of the reflex actions, or excito-motory movements. Of this important function I have now briefly to inform you. Its system of nerves arise from the spinal cord, and proceed thence to all the organs and parts which are under its influence. Please to mark attentively, that by one part of their constituent fibres the reflex nerves communicate the impression of the exciting cause to the spinal cord, and by the other part of their fibres

they return or reflect the active or motory power from the spinal cord to the muscles it excites to action.

These reflex actions consist in muscular movements, which are caused by external impressions without any necessary exercise of the will, without consciousness, and without sensation, in the healthy state.

I will state the principal parts and movements of the human body which are under the rule of the reflex function. This, indeed, will give you the best understanding of its nature. Firstly, then, I specify all the hollow organs, as, the stomach and bowels, in the propulsion of the food downwards; the bowels and the bladder, in the expulsion of their contents; the heart, in its work of the circulation of the blood; the lungs, in respiration. And we have reflex action of the gullet, in swallowing; of the eyelids, in winking. Further, the inlets by which food and air enter the body, and the outlets by which the excretions are expelled, are partly subject to reflex action; and in some measure, also, to that of the will.

But you must recollect, that this reflex action of organs and muscles concerned is always produced by special agents or excitants; and the motory power is always reflected or returned from the spinal cord. There are also modifications of these exciting causes, which must necessarily modify reflex action; and this may take place under different degrees of volition. For instance, by contact of the morsel of food with the fauces, or top of the gullet, we cause deglutition or swallowing, which is partly a voluntary act; whilst the contact of the blood in the heart causes its contraction without our consciousness.

When the exciting causes are abnormal or morbid in their nature, they give rise to irregular or convulsive action, which is always in connection, directly or indirectly, with the spinal cord. Worms, or other irritating causes in the intestines, especially in children, give rise to convulsions; also irritation of the gums in dentition or teething; and all similar causes act through the reflex nerves on the spinal cord, and not on the brain, as is often supposed. I may also allude to the action of certain poisons which are absorbed into the blood, especially strychnine.

In causing most violent convulsions this poison acts through the blood on the spinal cord, which, as already stated, is the source of nervous power for muscular action of all kinds. The poison of hydrophobia acts, also, through the blood.

From certain ganglia or nervous centres, placed on the anterior surface of the vertebral or spinal column, are sent off the sympathetic or organic nerves. These have free communication with the spinal nerves, and with other ganglia that lie amidst the abdominal organs, as well as with others which are placed at the base of the heart. And in the head we find also many other scattered ones belonging to the same system, and communicating with the nerves of the brain, and connected with other ganglia in the neck. You must mark attentively, that the nerves proceeding from these nervous centres are not distributed to the skin and muscles, like those of the reflex function already described to you, but to the organs of digestion and secretion, to supply nervous power for the performance of their functions; and to the heart and lungs; also to the walls of the blood-vessels, which they accompany throughout the entire body for the special purposes of nutrition, secretion, and excretion. You must further recollect, that the same kind of ganglia or nervous centres, with their nerves, are supplied to the other organs and parts of the body, and are named according to their locality; as the thoracic, the lumbar, the sacral ganglia. Through their branches of nerves they freely communicate with each other, and with the other systems of nerves. Indeed, this organic or sympathetic system has the special office of connecting all the organs and parts of the body in the sympathy and harmony of health; and in painful association in disease. I have already alluded to this sympathetic, or organic, or ganglionic nervous system as the source of organic nervous power, or curative force, and which acts such an important part in the animal economy, and to which I shall have to make frequent allusion in these letters. You will please, therefore, to consider and remember the statements I have made concerning it.

I feel sorry in being compelled by my limited space to refrain

from a more minute account of the anatomy and physiology of the three nervous systems of the human body. They strikingly display to us the sunbeam evidence of Divine benevolence, and Divine creative wisdom, and perfection of design. I here bethink me of the philosopher of old, who fell into the clutches of that accursed conclave, misnamed the Holy Inquisition, 'whose tender mercies are cruel." He was accused of atheism. When brought before them to answer to the accusation, he took a glance around him; and then taking up a straw, which had stuck to his tattered robe whilst on his miserable pallet in the dungeon, he held it up and exclained, "This is sufficient to convince me of the existence and omnipotence of God." True enough, dear Sir, were the words of that philosopher. But when we look on the exquisite structures, and uses, and adaptation of such parts of the human frame as are presented to us in the nervous systems, how stolid and depraved must be that mind that can fail to perceive the overwhelming evidence of the adorable attributes of the great Creator!

The nervous systems of man, the animal and the organic, and all the functions of the body performed through their instrumentality, are most intimately connected, and they act reciprocally on each other. Mark, then, that you may regard them as a circle of influences, at any point of which circle derangement and disease may commence. Thus, any part of it may become the primary seat of disease. Disease may arise from causes affecting the mind, or animal system of nerves. It may arise from causes affecting the organic nerves or their centres, the ganglions; or affecting the function of digestion in the stomach; or in the more advanced stages of assimilation of food; or affecting respiration; or nutrition in its last stage of change of tissue. Disease may arise from causes affecting directly any of the collateral functions of absorption, secretion, or excretion. I shall explain these three functions to you anon. Yet all these functions vary in their comparative power to affect each other. You must consider organic nervous power as the first one in the list, and whose derangement is most