A treatise on localized electrization, and its applications to pathology and therapeutics

Front matter

No. 3j ^ o />T

Boston

Medical Library

Part I. — Static Electricity .. .. .. .. .. .. . . 4

§ I. Physiological properties . . . . . . . . . . . . 4

A. Electro-positive and negative baths . . . . . . . . 4

B. Sparks and the Leyden jar . . . . . . . . 5

§ II. Therapeutical properties . . . . . . . . . . . . 7

Note by the Translator . . . . . . . . . . . . 9

PART II. — Contact Electricity (Galvanism) . . .. .. .. . . 10

§ I. Physiological properties . . . . . . . . . . . . 10

§ IT. Therapeutical properties . . . . . . . . . . . . 14

Part III. — Induced Electricity .. .. .. . . . . . . 17

§ I. Physiological action of the current of the first helix, and of the

current of the second helix . . . . . . . . . . 22

§ II. Therapeutic properties of induced currents . . . . . . 82

Different denominations of the various kinds of electricity . . 36

Note by the Translator . . . . . . . . . . . . 37

CHAPTEE II.

Localized Electrization.

Part II. — Localized Muscular Electrization

§ I. Localized muscular electrization by static electricity § II. Muscular electrization by contact electricity I. Voltaic Batteries for Medical Purposes

A. Batteries of large surface with inconstant currents The columnar pile of Volta

Cruikshank's trough battery The cylindrical glass battery Porcelain trough battery Wollaston's battery Berzelius's battery

B. Batteries of large surface with constant currents Daniell's battery

Grove's battery . . . . ■ . .

CONTENTS OF PART I.

Bunsen's battery

Parelles' balloon battery

Marie-Davy's sulphate of mercury battery

Marie'-Davy's sulpLate of lead battery . .

Siemens' battery (Remak's)

Note by the Translator : — (a) Stohrer's battery; (b) the Becker- Muirhead battery C. Portable batteries of small surface

Gaiffe's chloride of silver battery

Small columnar pile of the Conservatoire des Arts et Metiers

Note by the Translator: — Hammond's columnar battery ..

Galvanic chains of Golberger and Pulvermacher

Duchenne's ribbon battery

Mathieu's small tension-battery

Note by the Translator : — Foveaux's portable battery

Ruhmkorff s portable constant-current battery II. Operative Procedures for Localized Galvanization § in. Localized electrization by induced electricity, or localized muscular faradization I. The historic question II. Choice of an induction instrument

III. Choice of rheophores

IV. Indirect muscular faradization ..

V. Direct muscular faradization . .

VI. Excitability of nerves and muscles

A. Excitability of the motricity of nerves, and the contractility of muscles

B. Excitability of the sensibility of muscles

C. The points of selection in the practice of localized muscular faradization

51 51 52

55 55

69 70 71 72 73 74 79

80 82

Paet III. — Cutaneous Electrization .. .. .. .. .. .. 89

§ I. Electrization of the skin by static electricity . . . . . . 89

§ II. Electrization of the skin by dynamic electricity, or cutaneous

§ III. Electrization of the skin by the induced current, or cutaneous

II Mode of Operating

A. The electric hand

B. Solid metallic rheophores

C. Metallic threads Physiological and Therapeutical Action

Pabt IV. — Faradization of Internal Organs, the Genital Organs, and of the Organs of the Senses § I. Faradization of internal organs

1. Faradization of the rectum and muscles of the anus

2. Faradization of the bladder

3. Faradization of the uterus

4. Faradization of the pharynx and oesophagus . .

5. Faradization of the larynx Note by the Translator : — Ziemssen on laryngeal electrization

6. Faradization of the stomach, the liver, the lungs, and the

heart

90 90 90 91 91

93 93 93

94 96 96

97 98

CONTENTS OF PART I. 9

PAGE

7. Faradization of the diaphragm . . . . . . . . . . 105

8. Faradization of the intestines . . . . . . . . . . 105

§ II. Faradization of the organs of the senses .. — .. .. .. 106

§ III. Faradization of the male genital organs . . . . . . . . 108

Part V. — The General Effects of Localized Faradization .. .. 109

Chapter III

Historical and Critical Observations upon the Principal Methods op Electrization .. .. .. .. 114

Part I. — On the Value of Electro-puncture, as applied to the Treatment

Part II. — On the Value of Electrization by Reflex Action, as applied to

the Treatment of Paralysis . . . . . . . . . . . . 120

§ I. Passage of induced currents from the nerve-extremities to the

§ II. Excitation by reflex action in passing induced currents from

the mouth to the anus . . . . . . . . . . . . 127

§ III. Excitation of the innervation of the heart and respiratory organs by means of cutaneous faradization of the precordial region 134

I. In the treatment of asphyxia ... . . . . . . . . 134

II. In the treatment of grave functional disorders of the cardiac

circulation and the respiration, symptomatic of a dynamic central nervous lesion . . . . . . . . . . . . 137

Part III. — On the TJierapeutic value of Localized Faradization .. . . 147

§ I. Brief exposition of clinical facts, which establish that localized faradization is of great value in the treatment of atrophic paralysis .. .. .. .. .. .. .. .. 147

§ II. Critical examination of the electro-physiological experiments which have served as the foundation of the attacks recently directed against the therapeutic value of localized faradization 149 § HI. Upon what class of nerves does localized faradization exert its influence in order to increase the activity of the local circulation? .. 153

Part IV. — The Therapeutical value of Galvanization by Interrupted Currents, and by Continuous Currents, direct or indirect .. . . 173

§ I. Historical (early experiments) . . . . . . . . . . 173

§ II. Physiological action of continuous currents, direct or inverse, applied to the nerves of man, upon sensibility, or muscular contractility : — I. Duchenne's first experimental researches . . 175 II. The experimental researches of Eemak . . . . . . 173

§ III. Duchenne's latest researches on the therapeutic action of galvanization by interrupted or by continuous currents in the treatment of paralytic or nervous affections, as compared with localized faradization . . . . . . . . . . . , igi

Eesults of Duchenne's investigations into the therapeutic application of direct localized muscular galvanization by intermittent currents ...... 191

10 CONTENTS OF PART I.

PAGE

Results of Duchenne's investigations into the therapeutic application of reflex galvanization by continuous currents, mingled with feeble intermissions (labile currents), as compared with localized faradization .. .. .. .. .. ..193

A. Atrophic paralysis consecutive to traumatic lesions of

C. Electro muscular contractility .. ... .. .. 195

D. Paralytic contractions . . . . . . . . 197

E. Functional spasms, scrivener's palsy, neuralgic contrac-

tions called rheumatic, reflex ascending contractions from articular injuries, chorea . . . . . . . . 200

F. Progressive muscular atrophy . . . . . . . . 207

Galvanization by permanent continuous constant currents . . 208 The therapeutic action of galvanization of the skin, as compared

with cutaneous faradization . . . . . . . . . . 210

General conclusions . . . . . . . . . . . . . . 211

Ruhmkorff s portable constant-current battery . . . . . . 217

Note by the Translator : — Ziemssen on certain questions concerning the value of galvanic currents in medicine . . . . 219

CHAPTER IV. Electro-Medical Instruments with regard to their application

in Pathology, in Physiology, and in Therapeutics .. 232

Part II. — The Author's large Double-Current Volta-Faradic Instrument 243

A. Large volta-faradic instrument, closed (latest model) . . 244

B. Large uncovered instrument . . . . . . . . . . 247

§ II. Manner of setting the instrument in action . . . . . . 248

§ III. Theory of the instrument .. .. .. .. .. .. 251

Part HE. — Small Double-Current Volta-Faradic Instrument .. .. 266

B. Manner of putting the instrument in action . . . . . . 267

Part IV. — The Author's Double-Current Magneto-Faradic Instrument .. 269

§ II. Theory of the instrument .. .. .. .. .. .. 272

§ III. Explanation of its principal properties, and the different combinations which have governed its construction . . . . 274

§ IV. Manner of putting the instrument in action . . . . . . 283

Part V. — Historical and Critical Account of Induction Instruments . . 287

1. Magneto-electric instruments . . . . . . . . . . 287

Instrument of Faraday . . . . . . . . . . . . 287

„ Pixii 288

CONTENTS OF PART I.

Instrument of Clarke

PAGE

. 291

„ Page

„ „ Dujardin .. „ „ Breton freres „ „ Gaiffe

. 293 . 294 . 294 . 295

2. Electro-dynamic instruments Instrument of Kuhmkorff

. 296 . 296

„ „ Tripier ..

„ „ Du Bois-Reymond

„ „ Morin

. 298

. 299 . 300

„ Gaiffe

. 302

„ „ Trouve ..

. 306

„ „ Stohrer ..

. 320

§ II. Critical examination

. 307

1. Magneto-electric instruments

. 307

2. Electro-dynamic instruments . . . . . . . . . . 311

Note by the Translator: — Description of Stohrer's large and

small induction instrument . . . . . . . . . . 320

ON

AND ITS APPLICATIONS IN PATHOLOGY AND THERAPEUTICS.

Paet I.— METHODOLOGY.

LOCALIZED ELECTKIZATION.

Chapter I. Medical Electricity

Three varieties of electricity are employed in medicine — friction electricity, contact electricity, and induced electricity.1 The first is also called static electricity; the last two are included under the term dynamic electricity.

The first question which suggests itself with regard to them, the importance of which is self-evident, is as follows : — In their physiological and therapeutical applications, when it is desired to limit their action within certain organs, is it a matter of indifference which of the three varieties is employed ? In other words, are the physiological and therapeutical properties of the three varieties identical ?

I have no intention to set forth the various and discordant opinions which have prevailed upon this point. To do so would be to enter into historical questions, which I am desirous as far as possible to leave unnoticed. But I must observe that several physicians, who have made a special study of the therapeutical applications of electricity, have remarked certain differences between the properties of the static and of the dynamic form. Fabre Palaprat, for example, taught that static electricity was chiefly applicable to paralysis of sensation, ami to the excitation of the muscles of relation ; whilst, on the contrary, contact electricity was only adapted for the excitation of the muscles of organic life, or of delicate organs, such as the eye, the ear, &c.

These statements have been reproduced in many special treatises, although they did not rest upon any serious research ; and althouo-h, as I shall presently demonstrate, they were not in harmony with the physiological properties of the different forms of electricity. It is therefore not surprising that they should have been neglected

[' The two former varieties of electricity are now commonly termed by physicists franklinic electricity and voltaic electricity.

It is greatly to be desired that this terminology should bo adopted in works devoted to the medical application of electricity. — R. T.~]

B 2 in practice. It would be wrong, however, to suppose that the therapeutical action of electricity is always the same, whatever its source. I make no claim to have entirely solved this difficult question ; but I hope to establish that friction electricity, contact electricity, and induced electricity possess special physiological and therapeutical properties, and that each of them will fulfil particular indications.

Part I. STATIC ELECTRICITY

§ I. — Physiological Properties.

The principal methods employed for the application of static electricity are, as is well known, electrization by simple contact, called the electric bath ; electrization by sparks ; and, lastly, electrization by the Leyden jar. The other methods do not appear to me sufficiently important to require discussion.

A. — Electro-positive and Negative Baths.

The electric bath has long been ranked among the most valuable therapeutical agents. According to Giacomini,2 the positive form is applied and acts in the following manner : — " The patient, being insulated, is placed in contact with the conductor of the electrical machine. The whole surface of the body is thus electrified, while the air which surrounds the body is rendered electro-negative. The positive electricity by which the organism is charged is confined to the surface, and probably accumulates in the skin, by virtue of the law above-mentioned^ for it has no effect upon any internal organs. Neither the pulse, nor the secretions, nor the intellectual functions, nor the respiration, undergo any particular change ; and the accumulated electricity which constitutes the bath, escapes from all points of the epidermis, from the hair, beard, and nails," &c.

Giacomini attributes a hyposthenic influence to the electro-negative bath, which withdraws from the body a greater or smaller quantity of its natural electricity. This is done by insulating the patient, and by placing his body, and especially the diseased part, in connection with the cushion or rubber of the machine. The plate, being then turned, discharges vitreous electricity in proportion as it has accumulated. It is evident, according to Giacomini, that the electricity yielded by the cushion is derived from the nerves of the patient, instead of from the ground, as in the case of the positive bath.

2 Cited in La Bibliotheque du Medecin Practicien. Paris, 1850. Vol. xiv. p. 90.

STATIC ELECTRICITY. 5

This electro-physiological theory has certainly not been founded upon experiment; for a healthy person, subjected to an electric bath, either positive or negative, does not exhibit any symptoms of an influence either excitant or hyposthenic.

B. — Sparks, and the Leyden Jar.

Whatever may be the form of exciter that is brought into connection with the conductor of an electric machine, and whatever may be the distance that separates this exciter from the skin, the electricity furnished by the machine in action will reunite with that of the body at the epidermic surface, with a greater or less degree of tension. A pointed exciter allows the electricity to escape easily; with a knob the tension is greater and the sparks are less frequent ; but each of these forms discharges itself by a single spark. An exciter having a plane surface discharges itself by several sparks at once (from two to five), if it be at a little distance from the skin.

A metallic brush acts, in this respect, like a plane surface : that is, it gives off only two or three sparks at a time, whatever the number of threads of which it is composed.3

Static electricity applied by the exciter — of which the several actions have just been described — produces always the same sensations, differing only in their degree. These sensations may be compared to those produced by the impact of a small substance striking upon the skin. They are always disagreeable, however weak the electric tension. The feeling is never very acute, nor like that of a bum, or a puncture, whatever form of exciter may be employed. After a time the skin reddens and becomes more sensitive. To render the discharge more painful, it is necessary to employ a degree of tension that can only be obtained by a Leyden jar of moderate size, sufficiently charged ; but then the excitation will be no longer limited to the skin, and will produce the effects to be described hereafter.

Under weak tension, the action of static electricity can always

3 A brush of badger's hair has been determine a current of air to the surface used as an exciter ; and this, being in of the brush. It is this current, analogous connection with an electric machine, and to that which is formed at the surface of being held at a short distance from the the plate of an electric machine in moveskin, occasions a sensation of coolness ment, which causes the sensation of cooland a very slight pricking. Such a ness produced by the vicinity of the brush, itself a bad conductor, is charged ; electrified brush of badger's hair. It is with positive electricity, the excess of j evident that this method of electrization which escapes from the extremities of the \ is illusory ; since the natural electricity hairs, to unite with the electricity of j of the body undergoes no appreciable inthe surrounding air. The effect is a series fluencc. of rapid and successive re-unions which be limited to the skin. Such is the tension obtained from an electric machine of medium power: which is hardly enough to produce contraction of the superficial muscles, especially if the cellular tissue be rather abundant ; and, if produced, the contractions will be incomplete.

Although it is possible to confine the action of static electricity to the skin, it is not possible to concentrate its power upon the muscular tissue or upon the sub-cutaneous nerves. In fact, the superficial action of this form of electricity is inseparable from its deep action. In the latter the electric recomposition is still effected at the epidermic surface, and produces a cutaneous sensation that obscures the muscular.

The tension obtained by means of a Leyden jar enables the current to penetrate through a considerable thickness of tissue. Thus the current from the jar is sufficient to produce energetic muscular contraction ; but however feeble may be the tension, so long as it can be measured by Lane's electrometer, it always produces a shock, that is to say, a contraction and a sensation which extends beyond the point excited, and which is felt most acutely in the nervous centres.

If the exciter be placed over a nervous trunk, the sensation is like that produced by a severe contusion of the nerve, and is followed by a numbness that extends almost to the ultimate ramifications. With a sufficient degree of tension, acting either upon a nerve or upon muscular tissue, the shock is so strong that the whole limb, or even the whole body, seems as if struck by lightning.

At the spot at which a Leyden jar is discharged, the skin gradually loses colour over an area of two or three centimetres in radius, and becomes of a dull white in a few seconds. The nervous papillae stand erect upon the blanched surface, which is also somewhat lowered in temperature. The person on whom the experiment is tried sometimes experiences a feeling of numbness. Analogous phenomena appear to take place in the muscular tissue subjacent to the portion of skin that is acted upon. I have had occasion to make an electric discharge upon the surface of a denuded muscle, and this muscle lost somewhat of its colour, over a small space, for some time. The cutaneous local phenomena last generally from twenty to thirty minutes ; and once, in a delicate person, I saw them continue for three-quarters of an hour. After this time, the blanched spot passes, in a few minutes, from a dull white to an erythematous redness, and undergoes an elevation of temperature appreciable by the thermometer, and sometimes by the sensations of the patient.

STATIC ELECTKlCiTY. 7

It is universally known that the discharges of static electricity are very small in quantity ; and that for this reason their calorific and electrolytic effects are feeble.

Finally, the exciting action of the negative pole is greater than that of the positive, as is also observed in galvanic electricity.4

The organic phenomena just described appear to me to establish : (1) that the discharge of a Leyden jar produces at first, locally, a profound torpor, by suspending, for a time, the capillary circulation, and by diminishing the calorification in the tissues upon which it acts ; (2) that the excitement produced by this method of electrization is only a kind of reaction, as shewn by the erythematous redness, and by the augmentation of temperature in the parts formerly bleached ; (3) that the reaction is established with different degrees of facility.

§ II. — Tlierapeutical Properties.

The electro-positive bath, formerly used as a general excitant of the surface of the body, is now commonly abandoned, its therapeutical being as little discoverable as its physiological action.

It is not the same, it is said, with the electro-negative bath, which is ranked by the Italian school among their most valuable hyposthenisants. According to Giacomini, the patient subjected to this bath is de-electrized, is consequently deprived of a greater or less quantity of a stimulant analogous to heat, and undergoes a real hyposthenisant effect. Erysipelatous tissues may be seen to become blanched under its influence ; and chronic inflammations undergo an unquestionable improvement. Headaches, and neuralgic pains, have been instantly relieved by this kind of electric flux, as by the application of ice, which abstracts heat, and perhaps, at the same time, electricity also. Such are the virtues attributed to the electro-negative bath.

This notion of an electric flux may impress the imagination ; but it is difficult to believe that the hyposthenic effect is less doubtful than the excitant property once attributed to the positive bath. It would, however, be wrong to condemn a therapeutic agent solely on the ground of the nullity of its physiological action, especially when it is supported by an authority so great as that of Griacomini. It is therefore necessary to determine by fresh trials what is the actual value of the electro-neo;ative bath.

4 This important fact was discovered I siologiques produits par V electricity transby M. Cliauveau, the Director of the J mise dans Vorganisme animal a Ve'tat de anatomical and physiological courses at j courant instantane', et a Ve'tat de courant the Imperial Veterinary School at Lyons, j continu.' See his memoir: ' The'orle cles effets phy- \

Electrization by sparks produces a sensation analogous to that of whipping, and appears principally adapted for cases in which it is necessary slightly to stimulate the skin ; although it would be insufficient if very active stimulation were desired. In fact, to obtain such active stimulation, it would be necessary to have recourse to static electricity of high tension, such as would be furnished by the Leyden jar, and which would also produce such muscular contractions and general shock as to complicate the action upon the skin, and to contra-indicate the employment of the agent. Electrization by sparks is, therefore, useless in cases of profound and obstinate anaesthesia, or where it is wished to produce an instantaneous revulsion, such as would be effected by the actual cautery.

Electrization by sparks, even when they are yielded by a powerful machine, and by spherical exciters, is only able to produce contraction of some superficial or very excitable muscles, such as the platysma, the upper half of the sterno-mastoid, the margin of the trapezius, and some muscles of the face. In order that static electricity may affect the muscles generally, especially when they are covered by an abundance of cellular tissue, it would be necessary to employ a high tension by means of a Leyden jar. But the resulting shock, which would possibly extend to the nervous centres, would render such an operation dangerous or impracticable.

The knowledge of the local organic changes produced by the discharge of a Leyden jar enables us better to appreciate the therapeutic action. It has been already shewn that an organ so electrified only undergoes excitation after having suffered, for some time, from all the effects of torpor. It is easy to conceive that if any organ were exposed to discharges too frequent or too powerful, or if its vitality were already depressed, the stage of electric torpor might be indefinitely prolonged.

However favourable may be the conditions under which it is attempted to practise muscular electrization by the Leyden jar, it will always be imprudent to expose the patient to many discharges. Hence it would be impossible to electrify all the muscles in cases of paralysis of one or more of the limbs.

Moreover, the operation is always painful ; since the cutaneous excitation inseparable from the use of static electricity increases in proportion to the increase of tension.

It appears, then, on the whole, that the excitation of muscles by static electricity ought generally to be excluded from practice, and the more so since it may be replaced by another electric agent, which will be described in the third section (induced electricity) ;

STATIC ELECTRICITY. 9

and which excites muscular contractility and sensibility in a more energetic and effectual manner than the former, without any of the inconveniences that I have described. I purpose to point out in the sequel the cases in which its employment will be useful or necessary.

It is, however, incontestable that static electricity, which for many years was used exclusively in medical practice, has wrought some cures seemingly marvellous. These results shew only that certain paralyses are always cured by electricity, in whatever form and manner it may be employed. Unfortunately, these cases have been so rare that this mode of using electricity has not borne the test of time, and has been many times laid aside by physicians after having been taken up with some degree of enthusiasm.

[Friction electricity is used somewhat largely at the National Hospital for the Paralysed arid Epileptic. It has been found in the practice of this Hospital, and in private cases coming under my own observation, of considerable value in the treatment of the following affections : —

(a) Facial Neuralgia, which has resisted other modes of treatment, is occasionally relieved with rapidity, and permanently, by drawing sparks along the tracks of the affected branch or branches of the trifacial nerve. Occasionally also, but less commonly, electrization by sparks has partially or altogether relieved obstinate sciatica.

(b) Facial Spasm. — A remarkable instance of the effect of electrization by sparks in relieving facial spasm (tic convulsif) occurred in the case of a hospital patient under the care of Dr. Radcliffe. The patient was a female forty-eight years of age, and she had suffered for thirteen years from spasm of the muscles of the left side of the face. The distortion produced by the spasm was very great, and was apt to be so much exaggerated, by slight emotion, even such as would be caused by having to address a stranger, as to make speaking difficult, and to prevent proper attention to her occupation as a small shopkeeper. Dr. Eadcliffe directed an experimental trial of electrization by sparks along the lines of the nerves distributed to the affected muscles. After the third application the spasm was manifestly relieved, the distortion being, diminished, and the consecutive paroxysms occurring less frequently. By persisting with this treatment thrice weekly over a period of two months so great an amount of relief was obtained that little distortion of the face remained, and the patient was able to pursue her business with comfort.

(c) Hysterical Aphonia. — Electrization by sparks over the larynx has proved in the practice of the hospital so effective in the relief of cases of emotional aphonia, even those of long standing, that it is now almost invariably used in the treatment of these cases before having recourse to induced electricity. In six or seven recent cases, electrization by sparks repeated twice or thrice effected a complete cure. One of these cases was of nine, another of six months' duration. The remainder had lasted from four weeks to three months. The seventh case did not receive any benefit from the use of static electricity, and the other forms of the agent proved equally ineffective. The case recovered slowly under general treatment.

(</) Hysterical hyperesthesia, — Electrization by sparks over the affected spot has often proved of great benefit in removing the localized excessive sensitiveness not unfrequently found in hysterical cases, particularly in the spinal region.

(e) Tremor, whether general or local, is sometimes largely relieved by insulating the patient, and charging liini with positive electricity for a period of from twenty minutes to half an hour. For an examination of the probable influence of friction electricity in the treatment of painful and spasmodic affections consult Dr. Radcliffe's ' Lectures on Epileptic, Spasmodic, Neuralgic, and Paralytic Disorders of the Nervous System.' — H. T.~]

Part II. CONTACT ELECTRICITY (GALVANISM)

The term dynamic electricity, that is to say, electricity in motion, has been used to denote the electricity produced by contact (galvanism), and the electricity caused by induction. This form, obtained from voltaic piles, or from an electro-magnetic apparatus, possesses physiological and therapeutical properties essentially different from those of static electricity.

The most important property of dynamic electricity, regarded from a physiological or therapeutical point of view, is that by which its action can be directed to, and limited within, almost any organ of the body. It is shown, indeed, by my experiments, that we may at pleasure confine this agent to the skin, or may cause it to penetrate the skin, without puncture or incision, and may limit its action to the subjacent organs, the nerves, the muscles, or even the bones. Of this I shall give evidence in the sequel.

The cutaneous sensation produced by dynamic electricity may range from a simple titillation to the most acute pain. The excitation thus produced may always, by the use of special means, be confined entirely to the skin, whatever be the power of the current.

The same electro-dynamic force, directed upon a muscle, or upon a nerve-trunk, has power to produce the most energetic muscular contraction, without any of the general shock that characterises the action of static electricity, and that usually forbids its employment.

Such are the principal effects to be obtained from dynamic electricity, which includes contact electricity (galvanism) and induced electricity.

But each of these forms of dynamic electricity possesses special properties, physical, chemical, and physiological, such as to prevent them from being employed indifferently in practice. These special properties may even fulfil certain determinate indications, and they therefore require to be separately considered.