Organic and functional nervous diseases; a text-book of neurology

Front matter

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Chapter I

INTEODUCTOEY. THE GENEEAL DIAGNOSIS OF NEEVOUS

DISEASES.

THE METHOD OF EXAMINATION OF A PATIENT.

The multitude and variety of symptoms which are present in nervous diseases are frequently bewildering and render it difl&cult for the student to know how to examine a patient suffering from a nervous disease. Some suggestions regarding methods of examination are necessary, and when each symptom is elicited by this examination the significance of each symptom or group of symptoms will be discussed.

It is important in every case to obtain a complete history of the patient before proceeding to the physical examination. This history should elicit the hereditary tendencies of the patient, for the family history often affords an important clue to the disease present. Alcoholism or drug addiction, chronic lead or other poisons, such diseases as gout, tuberculosis or anaemia, as well as the various nervous diseases in parents make the liability to nervous affections in the next generation greater, and are often the cause of functional affections, such as epilepsy, neurasthenia, psychasthenia and the tics. There are some diseases which run through several generations in a family, and which seem to imply some defective capacity of development. Thus hereditary deafness and blindness ; the dystrophies affecting the muscles ; the forms of ataxia seen in Friedreich's disease and in Marie's cerebellar atrophy, and juvenile spastic paraplegia are all examples of what Gowers has termed abiotrophy, a congenital tendency for the special organ or part of the nervous system involved to wither and die long before the life of the individual ends.

The personal history of the patient should be carefully studied, for the development in early life of convulsions, of headache, of habit spasms, of fainting fits, of mental peculiarities, or mental defects will 2 17

18 THE GENERAL DIAGNOSIS OF NERVOUS DISEASES.

show a state of weakness of structure or error of function in the brain which may be a cause predisposing to the occurrence of nervous disease in later life. There are many nervous aifections directly or indirectly traceable to bad habits, to alcoholism, to chronic toxaemia by drugs or metals or poisons, to the infectious diseases and to syphilis. That many nervous aifections appear as a sequel of infections is now well known ; the neurasthenia and psychasthcnia following the grippe being examjiles. Sometimes the occupation of the patient will at once lead to the diagnosis ; as in lead palsy or in writer's or telegrapher's cramps, or in the paraplegia developing in those who work in caissons. There are not a few cases of nervous disease, both organic and functional, which are due to injury or to its attendant mental shock. And the influence of care, anxiety, and long-continued worry and overwork of a mental kind is fully appreciated by all physicians as a cause of nervous disease.

The history of the mode of onset of the affection in question is equally important. The sudden appearance of symptoms, trauma being excluded, suggests some primary vascular disease, as in apoplexy ; or some acute infection, as in infantile paralysis or chorea. The gradual onset is characteristic of the more slowly advancing sclerotic changes, in the nervous system which cause so many forms of progressive paralysis ; while the possibility of tumor growth should never be overlooked as a cause in these cases. Lastly it is not to be forgotten that many nervous symptoms are wholly secondary to and the result of diseases of other organs, as for example the headaches from eyestrain, the reflex neuroses, neurasthenia of pulmonary or gastric or intestinal origin, hysteria from ovarian disease.

The most prominent symptoms related by the patient will as a rule indicate whether the affection is functional or organic. The fact of occasional complete intermission in these symptoms is itself suggestive of functional disease, as in neuralgia as contrasted with neuritis, as in epilepsy, or in the spasmodic neuroses, as contrasted with the permanence of paralysis or of contracture or of ataxia. The extreme variability in the character and in the intensity of symptoms, such as is seen in neuralgia, iu neurasthenia, and in hysteria, is at once suggestive of a functional disease : for when organic changes have occurred in the brain or in the spinal cord the symptoms are not only permanent but are invariable. And the susceptibility of a patient to various physical or psychical impressions or remedies is also an indication that the symptoms do not depend upon destruction of nerve tissue. Thus the history of the chief complaints and of their mode of appearance and constancy will usually give a clue to the form of disease present.

If that disease is clearly organic in nature there is rarely any difficulty in assigning it to the part of the nervous system primarily involved. Lesions of the nerves produce pain, paralysis, anaesthesia and trophic symptoms wholly different in their exact locality and distribution in the body from lesions of the spinal cord, and hence by the grouping of the symjjtoms rather than by differences in their kind a differentiation mn QENEBAL DIAGNOSIS OF NEBVOUS DISEASES. ' 19

between nerve and cord lesions is reached. Lesions of the spinal cord produce" symptoms wholly different in their distribution in the body from lesions in the brain, one being as a rule bilateral, the other unilateral ; one being attended by electrical changes in the muscles and a loss of reflex action in the muscles, the other not. Lesions of the brain produce many changes in mental activity, in consciousness, memory and temper, in the powers of thought, expression and action, in the use of the cranial nerves, in the gait and balance never seen in disease of the nerves or of the spinal cord. Thus a cursory examination at once directs the attention of the examiner to the portion of the nervous system chiefly affected.

The objective examination to determine the exact character, extent, and location of each symptom ; and to ascertain the actual degree of incapacity of every function is more important than the history. During the progress of such an examination incidentally the character and temperament of the patient, his emotional condition as shown in his facial expression, attitude, and manner of conversation, his degree of intelligence, his power of understanding, his capacity of speech, of movement, or of balance, can easily be observed without direct questions. Disturbances in the state of the mind, in the character and acuteness of the emotional control, in the rapidity of mental response to questions and impressions, and in memory are symptoms which are to be elicited by observation, as. the patient may be unaware of them, and unable to judge of his own condition. Powers of expression, the capacity to weigh and judge matters, the prevailing mood, are all important indications of the mental state ; and can sometimes be learned better from relatives than from the patient. Hence the views of those with whom he lives are always to be obtained.

In a case of shaking palsy, or of hemiplegia, or of locomotor ataxia, or of spastic paraplegia, mere inspection as a patient walks into the office is sometimes sufficient to warrant a diagnosis. But it is only after a thorough investigation of the powers of motion, of sensation, of reflex activity, of coordination, of gait, of speech, of mental activity and of self-control that one should feel sure that the entire ground has been covered in the examination.

The various symptoms presented by the various forms of nervous disease are fully discussed in the following chapters of this part, each symptom in affections of the nerves, of the spinal cord and of the brain being described, the manner in which these symptoms may be elicited being portrayed, and the significance of each symptom being indicated. The attempt is made to trace each symptom to its underlying pathological cause, so that the nature and situation of the lesion incidentally appears from the study of the symptoms. But as this necessarily implies a knowledge of the anatomy and physiology of the nervous system tlie essential and important facts of applied anatomy are included in the; chapters upon diagnosis.

If in the use of this text-book constant comparison is made between the symptoms described in each djs^ease and the discussioji of the si^--

20 THE GENEEAL DIAGNOSIS OF NERVOUS DISEASES.

nificance of those symptoms in the chapters upon diagnosis, a much more comjjlete view will be gained of the disease in question, and it will become at once apj^arent how a complete study of a symptom in nervous diseases usually leads at once to a definite conclusion as to both the character and the situation of the underlying lesion which causes it.

The use of the book will be enhanced by a constant reference to the index where, incidentally, the classification of the causes of the majority of symptoms appears.

As a working scheme for such a neurological examination the following is oifered.

Present complaint, with history of its onset and course.

Previous diseases, and habits, and injuries. Heredity.

Appearance, station, gait, power of motion or ataxia.

Investigation of each cranial nerve in order, with particular attention to the special senses and ophthalmoscopic examination and to the motion of eyes, face and tongue.

Examination for paralysis ; including state of reflexes of pupils and superficial and deep reflexes.

Examination for disturbance of touch, temperature, pain and muscular senses ; with particular care in the location of these or of all spontaneous pain or numbness.

Condition of speech, and intelligence and emotional state.

General physical examination of all organs.

Chapter II. The Structure Of The Nervous System

I. The Cerebro-spinal Nervous System. Neurones, Central and Peripheral. Dendrites. Axones. Terminal Tassels. Varieties, of Neorones. Nutrition and Pathology of Neurones. II. The Sympathetic Nervous System.

The nervous system is divided into two parts, the cerebro-spinal system and the sympathetic system.

I. THE CEREBRO-SPINAL NERVOUS SYSTEM.

The cerebro-spinal nervous system consists of two large central organs, the brain and spinal cord, and of a very extensive and wide-spread peripheral system of nerves which bring these central organs into communication with every part of the body. Inasmuch as every form of functional activity in the organism requires direction in accordance with the needs of each organ and also of the entire body, it is evident that a central regulating station in perfect connection with all the diiferent parts is a necessity. The cerebro-spinal nervous system supplies this need. Its function consists in the reception of impressions and the response to these impressions by actions that are performed in a properly ordered manner adapted to an end. Incidentally impressions and actions are registered, so that recollection is possible and repetition is easy. These acts may be unconscious and automatic, or conscious and voluntary, according to the parts of the nervous system which are called into play by the impression. But, whether conscious or unconscious, the action is always one of control of the lower mechanisms of the body ; of the sensory organs, and of the voluntary and involuntary muscles ; of the circulatory and respiratory systems ; of the secretory glands, and of the digestive and reproductive systems. Thus the nervous system may be considered as the governing and controlling system of the entire organism.

The central organs of the nervous system are made up of gray and white matter, whose visible difference led older anatomists to attach much importance to their varying arrangement. The gray matter was known to be made up of cells, and the white matter of nerve fibres transmitting impulses to and from the cells. But recent investigation has demonstrated that gray and white matter are merely different parts of elementary bodies, termed neurones, which make up the nervous system, and that the study of these neurones, of their structure, and of their connections, whether they lie singly or in groups, as in the spinal cord, or in masses, as in the basal ganglia of the brain, or spread

22 TEE STHUCTUEE OF TUE NEEVOVS SYSTEM.

out in layers, as in the cerebral cortex, is a matter of the greatest importance from every point of view. It is found that the white matter and tlie nerves are merely the distal portions of these neurones, and are not to be studied apart from the central part or body which forms the gray matter. It is therefore the chief object of the anatomist to-day to establish the situation of the neurone body and the course and termination of the neurone branches, their mutual relations, and their manner of action and interaction. (See Plate I., frontispiece.)

The neurones are held together by neuroglia and connective tissue, and are amply supplied with bloodvessels and lymphatics.

Classes of Neurones. — There are two classes of neurones different in their origin in embryonal life. The first class develops in the central nervous system. The second class develops in the ganglia, which lie upon the nerves.

I. The First ot Central Class of Neurone. — The neurone consists of a cell body and its projecting branches. These are of two kinds, dendrites and axones.

The cell body has various shapes in different parts of the nervous system, being spherical, pyramidal, and. polygonal, as shown in Fig, 1. The actual structure of the body is shown in Plate II, A, page 22, which demonstrates a protoplasmic mass unstained, a nucleus and nucleolus and a large number of granular bodies which are more or less regularly arranged in the protoplasm about the nucleus. These bodies are stained by basic aniline dyes and have been termed Nissl bodies, chromophile bodies, stainable substance, or tigroid. Nissl bodies are made up of phospho-albumin, and it is supposed that this exists in solution in the living cell among the other ingredients of the protoplasm, but is precipitated by the fixative and then stained by the dye. The cell body varies greatly in size in different parts of the nervous system ; it is from 4 to 135 microns in diameter. Through the cell body fine fibrils have been shown to pass in many directions from and to the branching processes.^ (Figs. 2 and 3.)

The dendrites are branching protoplasmic processes of the cell body and resemble it in structure. They are very numerous in some neurones. Near the cell body they are thick, but as they extend away they divide and subdivide, resembling the roots of a tree, until they end in fine fibrils. The dendrites vary in length, some neurones having one very long dendrite and many short ones. These variations are shown in Fig. 1. They pursue a tortuous course and are very irregular in their size, shape, and branching. The surface of the dendrite is rough and often nodular, and appears to be covered with small granules called buds or gemmules. Within the dendrite fine filaments lie

1 The reader is referred to Barker' s Nervous System, Appleton & Co., 1898 ; to Ewing, Studies on Ganglion Cells, Archives of Neurology and Psychopathology, 1898, vol. i., p. 263 ; to Bailey, Morphology of Ganglion Cells, Journal of Experimental Medicine, 1901, vol. V, p. 550 ; to Nissl, Die Neuronenlehre, Jena, 1903, and to Lewandowsky^ Handbuch der Neurologic, Bd. I, 1910.

THE CEREBROSPINAL NERVOUS SYSTEM.

Fig. 1.

Neurones, 1, anterior horn of sjiinal cord; 2, optic thaluiniis ; 3, posterior spinal ganglion (chick embryo); 4, cerebellum ; 5, cerebral cortex, surface layer.

24 THE STRUCTURE OF THE NERVOUS SYSTEM.

Fig. 2.

Large pluripolar ganglion cell of the ventral paramedian field of the abdominal cord of Lvmbriciis. A primitive fibril is seen on its way to a ganglion cell becoming thinner, owing to the emission of the side fibrils. A very complicated intracellular reticulum of neuro-fibrils is to be made out in the formation of which the primitive fibrils of all the processes take part, kk, nucleolus ; k, nucleus, a and /3 are processes containing one primitive fibril in each, which arriving in the cell body split up into several bifurcating neuro-fibrils. The primitive fibril in a can be followed for a very long distance, being thicker at a distance from the cell. The coarse longitudinal processes y and & contain a large number of primitive fibrils which, as far as they can be followed, do not unite to one fibril. (After S. Apathy, Mitth. aus der zool. St. zu Neapel, 1897, Bd. xii., Ht. 4, Taf. xxvii., Fig. 7.)

Fig. 3.

Cells of the anterior corpora quadrigemina of the cat, to show neuro-fibrils. A, axone ; B, plexus of neuro-fibrils made up of fibrils entering the cell from the branches ; C, perinucleur plexus of fibrils in a cell which has been divided longitudinally; D, fibrils running from the plexus into the branches. (Ramon y Cajal, Bibliog. Anat, 1904, p. 264.)

THE CEBEBEO-SPINAL NEBVOUS SYSTEM.

which pass into the cell body, and through it into other dendrites or into the axorie.^ These filaments are called neuro-fibrils. They were first demonstrated by Apathy in worms and have been more fully described in the hmnau neurone by Ramon y Cajal. (See Fig. 2.) It is supposed that the dendrites collect and transmit nervous impulses to the cell body ; and as they are niunerous and long it is evident that impulses from many sources may reach any one cell body.

The axone or axis-cylinder process of the neurone is a single, long

Fig. 4.

-xt

A, Cell dividpr' ] ".gitudinally ; B, surface of cell showing the "terminal feet " of Held, the manner of termination of the fine neuro-fibrils upon the surface of the cells. These fibrils come from a plexus of fibrils lying about the cells. (Ramon y Cajal, Bibliog. Anat., 1904.)

branch, arising from a cone-like projection of the cell body. This cone-like projection, as well as its base within the cell body, contains no chromophile substance, but fine fibrils can be found within it by acid stains. It is supposed to transmit nervous impulses from the cell. It is straight and smooth in contour. It undergoes a slight contraction soon after leaving the cell body, but then becomes larger and remains uniform in diameter. Though in its course within the central organs it gives oif very fine collateral filaments at right angles to its direction, it does not branch in the nerve until it reaches its very end, some distance from the cell body. There it divides into a number of little end fibrils resembling a tuft or tassel. (Fig. 7.) In the central organs it is possible that these fibrils enter the dendrites of other neurones. It is possible that they end in free terminations

^ Van Gehuchten.

March, 1905.

Le Ndvraxe, January, 1904. Cajal, Bibliographic Anatomique,

TTtE STBUCTUBE OF THE NEHVOVS SYSTEM.

which merely touch these dcDcl rites. It is also possible that they end on the surface of other cell bodies in what are known as the plates of Auerbach or the end feet of Held, but the exact connection is not yet determined. (See Figs. 3 and 4.) The collaterals terminate in the same manner. The termination of the axone in muscles is in the so-called muscle plate. In the other organs it ends in a fine plexus of nerve filaments. The axone is made up of many fine fibrils packed together, which are gathered from the cell body and from its dendrites.

Fig. 5.

Purkinje neurone of cerebellum. Many dendrites. One axone projecting from the body.

Fig. 8 shows this structure. The size of the axone at its exit from the cell body varies in different neurones. Some axones extend long distances, as from the cortex of the brain to the lowest part of the spinal cord. This variety is known as Type I. of Golgi. (Fig. 9.)

Some axones terminate near the cell body, dividing and subdividing mto-a sort of network. This variety is known as Type II. of Golgi. (Fig. 10.) Between these extremes all varieties are to be found.

When the long axones leave the gray matter they are insulated from each other by receiving a medullary sheath or fatty coating, held in place by a thin membrane, but this they lose at their termination. In Fig. 9 this is shown. Some axones on nearing their termination appear to split in two in a Y-shaped manner and each division has its own end tassel. If the nervous impulse passes out from the cell body

THE CE-REBnO-SPINAL NEnrOtJS ST.'^fEM.

S7 along the ax(>ne it is evident that it may reach many different destinations, because of tlie different places of ending of tlie collaterals and of

Fig. 6.

Neurones of the cerebral cortex, second layer. The long dendrite extends to the surface layer. Smaller dendrites go out from the body. The axons passes downward from the body, giving off collaterals.

TEE STBVCTVBE OF TEE NERFOUS SYSTEM.

Fig. 7.

Fig. 8.

The terminal fibres of the axones ; a, axone bifurcating near its termination ; 6, c, d, terminal brushes. (Eamon y Cajal, Studien iiber die Hirnrinde des Meuschen, I., 55.)

the terminal filaments. The terminal filaments of the axones are never continuous with other axones ; but impulses are probably conveyed from one neurone to another by the contact of axones with adjacent dendrites or with other cell bodies.

The nutrition of both axones and dendrites is controlled by the cell body, for they atrophy when separated from it. Nerves are the axones of neurones collected into bundles and held together by connective tissue.

II. The Second or Peripheral Class of Neurone. — This class belongs to the sensory part of the nervous system. It develops originally in the posterior spinal ganglia that lie outside of the spinal cord and in the homologous ganglia that are in Axone from the sciatic couuection witli the scusory crauial nerves and also nerve of a frog, showing in the ganglia of the sympathetic system. The fibrillary structure and a gensory ueurouc iu au early stage of develop-

node of Eanvier. (Ver- .'I'l i i • i n ii

^orn ) ment is bipolar, a branch coming out ol each end

of the cell body. (Fig. 1, 3.) Later the two branches appear to be fused together for a short distance, and thus in the adult the sensory neurone is pear-shaped and appears to send out a single axone which divides into two branches, passing in opposite directions. One of these branches finds its way outward to the periph-

TBE CEBEBEO-SPINAL NEFvVOUS SYSTEM.

ery of the body, forming a sensory nerve, and terminates in a fine brush-like Expansion of filaments in the skin or in the tactile corpuscles. The other branch finds its way inward through the posterior nerve into the spinal cord or brain axis, where it bifurcates, one

Fig. 9.

ft^s?

Scheme of central motor neurone, f I. type of Golgi. ) The motor cell body, together with all its protoplasmic processes, its axis-cylinder process, side fibrils, or collaterals, and end ramifications, represent parts of a single cell or neurone, a.h., axone-hillock devoid of Nissl bodies, and showing fibrillation; nx., axis cylinder or axone. This process, near the cell body, becomes surrounded by myelin, m., and a cellular sheath, the neurilemma, the latter not being an integral part of the neurone ; c, cytoplasm showing Nissl bodies and lighter ground substance ; d., protoplasmic processes (dendrites) containing Nissl bodies; »., nucleus; n.', nucleolus; n.R., node of Ranvier ; .v./., side fibril; n. of n., nucleus of neurilemma sheath; lei., motor end plate or telodendron; m.', striped muscle fibre; s.L,, segmcntatioD of Lanterraann. (Barker.)

30 TBE STEUCTUEE OF THE NEEVOUS SYSTEM.

portion passing downward and the other portion upward in the posterior columns of the spinal cord, or in the formatio reticularis of the brain axis. As these main branches pass up and down within the cord they give off at right angles little collaterals, and these collaterals,

Golgi's cell of Type II. from the dorsal horn of the gray matter of the spinal cord of the newborn mouse. Even in such a neurone the axone is very easily distinguishable from the dendrites. The lat^ ter are only represented in part in the illustration. (After von Lenhossek.)

together with the main branches, terminate in brush-like extremities within the gray matter of the posterior horn, either near their entrance or as far from their entrance as the posterior nuclei of the medulla oblongata, or at various levels in the brain axis. The sensory axone never terminates in a cell in the spinal cord or brain axis. It ends in brush-like terminations or tassels.

In this form of neurone the cell body is situated about one-half way between the terminal extremities of its two great branches, and this fact of the interposition of the body in the course of a nerve tract, which, from the nature of the case, must be a continuous tract, sug-

TEE CEBEBBO-SPINAL NEEVOUS SYSTEM. 31

gests that the function of the cell body is a trophic one. We have proof also t)iat an axone is not always centrifugal in the direction of its impulses.

The structure of the cell body in this class of neurones is not different from that in the first class ; but the chromophile granules are arranged about the nucleus in a series of concentric rings. (See Plate II., B., page 22.)

Varieties of Neurones. — Neurones have been classified into :

1. Primary neurones, whose cell bodies lie in the central nervous system or ganglia and whose axones extend thence to some peripheral part of the organism, to a muscle, or to a gland, or to the skin, or to some sensory organ, and

2. Secondary neurones, whose cell bodies lie in the central nervous system and whose axones extend to some other part of the central nervous system, to terminate about a primary neurone or about another secondary neurone.

Neurones have also been classified according to their function into

1. Centrifugal : (a) motor, (6) secretory, (c) trophic.

2. Centripetal or sensory.

3. Intrinsic or association.

The diagram (Plate I., frontispiece) illustrates these various neurones and their relations to one another.

Reflex acts may be performed by the primary neurones, but all conscious sensations or voluntary acts involve the action of both primary and secondary neurones acting together. This action may be illustrated by the analysis of a simple sensation, like the impact of a particle of dust in the eye, which causes a wink, a flow of tears, a conscious pain, and a voluntary effort to remove the particle. The sensation comes in from the eye along the primary sensory neurone, is transmitted (a) to the brain axis, where it reaches the primary motor neurone, setting up the centrifugal reflex acts of a wink and of secretion of tears, and (6) to the secondary sensory neurone, which transmits it upward to the brain. This secondary neurone may terminate about another secondary or association neurone, which then sends the impulse on to a secondary motor neurone, and this in turn sends its impulse down to the primary neurone, which transmits it to the muscle, causing the removal by the hand of the particle.

There are many more complex acts, either automatic, like the act of breathing or sneezing ; or voluntary, like the act of walking or talking, which call into play a vast number of neurones — centripetal, intrinsic, centrifugal — which cannot be so easily analyzed. But however complex the act, the physical basis of all nervous and mental activity is this series of neurones.

The arrangement of these neurones and their mutual relations will be considered in connection with the studies of diseases of the various parts of tlic nervous system. In that connection also the vascular supply of the nervous system will be described.

32 THE STRUCTURE OF THE NERVOUS SYSTEM.

The Nutrition of the Neurone. — In order that these neurones may do their work they must have a normal structure and a normal capacity lor sustaining their nutrition when in activity. When a neurone is made to work it undergoes certain manifest changes. Hodge ^ was the first to describe alterations in the form and appearance of the cell and of its nucleus consequent upon its activity. There is a general diminution in the size of the cell, a lessened power to absorb staining substances, which may be taken as a proof of the using up of its own substance and also changes in the appearance of the nucleus, which is decreased in size, and changes from a smooth and rounded outline to a jagged and irregular one. As the cell becomes changed in its structure by constant work, it becomes more and more exhausted, so that finally there comes a time when it is no longer capable of sending out impulses, and requires a period of rest to make up what it has lost of form and to regain a store of energy. Vas " and Mann ^ have described these physiological changes more exactly. Vas showed that mild stimulation of a cell caused a swelling of its body and of the nuclei and a clearing up of the central part of the cell by an apparent movement of the chromatin bodies to its periphery. Mann showed that functional activity of the cell is accompanied by an increase in the size due to imbibition of the lymph lying in the cavity about the cell, so that the cell at work fills up the cavity in which it lies. When activity goes on to the point of fatigue, then a shrivelling of the cell begins, first in the nucleus, then in the body. At the same time changes go on in the chromatin. During the period of activity the chromatin material is used up, so that a fatigued cell does not absorb staining material as does a cell at rest. In an exhausted cell the only stain is in and about the nucleus. In Plate II. these changes are shown. These results have been reached by stimulating cells to work in living animals either by electricity or by keeping up movements, such as running, or by exposing one eye to the light while the other was kept dark, and then contrasting the appearance of the cells made to work with those that were kept at rest. When a stimulated cell is allowed to rest it gradually resumes its original appearance ; but the period of rest must be adequate. During the period of reconstruction the chemical activities going on in the cell are numerous, and its power of assimilation of material furnished to it by the blood must be increased. If, however, anything interferes with this increased nutrition, such as an imperfect supply of blood or a deleterious substance of any kind in the blood, then the process of building up fails to take place, and the neurone cannot resume its function.