A text-book of electricity in medicine and surgery for the use of students and practitioners

Front matter

YALE MEDICAL LIBRARY

in memory of

VERA SCHWEITZER

Contents

I. PRINCIPLES 1

II. Batteries 27

III. Physiology 45

Chapter I. Principles

We think it advisable, before touching on any of the various details of our subject, to endeavour to give the reader some general notion of the place which electricity should hold in the catalogue of Materia Medica. We may begin by asserting that no other single artificial therapeutic agent is so generally useful, or admits of so many and such varied applications. An electric battery in the hands of a medical man, who has mastered some of the first principles of electricity, is capable of being turned to a great variety of uses, some of which undoubtedly may be better performed by many other agents which we have at our command. For others it stands alone and supreme, and will occasionally help a patient on his road to recovery when everything else has failed to render him the slightest service. Electricity apparently has the power of evoking function in every form of living tissue, and this power entitles it to a high place amongst those remedies which we call stimulants. It has hitherto been chiefly employed in medicine as a stimulant to muscular tissue, and a great part of the ensuing volume will be found to be devoted to this application of electricity. It is likewise a stimulant

B to nervous tissue ; and motor and sensory nerves, nerves of special sense, and the nerve-centres themselves, all readily respond to the electrical stimulus. Tissues which are not so intimately connected with the nerves are also influenced by electrical currents, and there is no doubt that, by their judicious application, nutritive processes may be modified, and the rate of secretion of certain glands (salivary, &c.) be quickened.

Like many other stimulant medicines, electricity has also very marked anodyne and soothing qualities, and its reputation as a remedial agent is based very largely on its great power in this direction. The chemical effects of electricity, and its power of decomposing compound fluids, have caused it to be used for dissolving tissues, and indeed its caustic action is not excelled by any of our ordinary escbarotics. It has also a marked power in bringing about the coagulation of the blood, and for this end it has been used in the treatment of aneurisms. Surgeons have found in electricity a convenient and manageable source of heat, and at present the galvanic cautery takes a recognised and acknowledged place amongst surgical instruments. To those who ask, What are the uses of electricity in medicine ? we may reply that, according to its method of employment, it may be a stimulant, anodyne, sedative, caustic, styptic, or cautery.

Electricity is used in medicine, not only for its therapeutic power, but also on account of its value as a means of diagnosis. By it we are often enabled to decide as to the seat or nature of a paralysing lesion ; the electric probe has enabled surgeons to speak with certainty as to the presence of bullets in wounds, and it is possible that in the thermoelectric pile we may some day find a practical and accurate means of determining the temperature of the surface of the body.

Writers on Materia Medica are accustomed to deal, firstly, with the natural history of every therapeutic agent, its source of origin or its mode of manufacture ; secondly, they pass to a consideration of its physiological action, and from, the physiological facts they are accustomed, in the third place, to deduce certain rules for our guidance as to its therapeutic employment. We shall follow a similar course in this work ; and although it is to be feared the reader will find that the basis of electro-therapeusis is empirical rather than physiological, we should not on that account be justified in disregarding the facts which have been established as to electro-physiology.

Electricity has been used in medicine in its three most usual forms. First, in the form which is generated in so-called batteries, and which has been called the hattery current, or, in honour of its discoverer, Galvanism, or, in honour of its chief investigator, Voltaic electricity, or, by reason of its usual method of employment, the continuous current. Secondly, it has been employed — and largely employed — in the form of the ' induced current ; ' the form which has been named, after our countryman, Faradism, and which, from its usual method of employment, is not uncommonly spoken of as the interrupted current. Thirdly, it has been employed in the form of frietional electricity, such as is generated by the friction of glass discs, or cylinders, and which has also received the name of static electricity, or, in honour of its chief original investigator, Franldinism.

These three forms of electricity generated from batteries, or by induction, or by friction, and which we shall speak of as Galvanism, Faradism, and Franklinism, are to be kept distinct in the mind, and — being employed, as they are, for widely different purposes — must no more be confounded together than the three narcotics, opium, chloral, and Indian hemp.

In dealing with a subject like this, nothing is so important as to begin really at the beginning ; and since some knowledge of electrical principles is absolutely necessary for the proper comprehension of the subject with which we have to deal ; and since, at present, electricity is not one of the sub-

b 2 jects a knowledge of which is usually required of the legally qualified practitioner, we feel that no excuse is needed for detaining the reader a short time with the consideration of some first principles. Surely it is better to run the risk of telling him that which perhaps he may already know, than to leave him uninformed upon certain points which necessarily constitute the very foundations of our subject.

Galvanism, or the battery current, owes its origin to chemical action, which is allowed to take place in a series of cells.

The galvanic cell in its simplest form consists of two plates of different metals immersed in a fluid which is capable of acting chemically upon one of them, or which, if it exerts a chemical action upon both, affects one more powerfully than the other. When the two metals so immersed are connected together by a wire, a current of electricity passes along the wire ; and if a galvanometer be interposed in the length of the conducting wire, its needle will be deflected, thus giving proof positive as to the existence of an electric current.

The simplest form of the galvanic cell consists of a plate of zinc and a plate of copper immersed in dilute sulphuric acid, and connected by means of a copper wire. Thus our conditions are fulfilled, since dilute sulphuric acid exerts a powerful chemical action upon zinc, but none, or next to none, upon the copper. The zinc plate, being the one which is chemically acted upon, is called the generating plate of the battery, while the copper is spoken of as the collecting plate of the battery. It is important to remember that the electric current takes a definite direction, and that it always travels in the cell, from the generating to the collecting plate, from the zinc to the copper, and, consequently, outside the cell, it continues in the same direction, in order to complete its circuit, and travels from the copper to the zinc. If the connecting wire be cut in two, that end of it which is joined to the copper plate is called the positive pole, and that end which is joined to the zinc plate is called the negative pole. It is important to remember that the current invariably travels from the positive to the negative pole, and it will be found, when we come to speak of therapeutics, that a knowledge of this fact niust be constantly borne in mind.

A nnmber of cells, such as we have described, may be united in a series, the copper of one being joined to the zinc of the next, and in this way a battery of any size may be constructed ; or, in other words, a battery of any number of elements, and the strength of a battery is, coeteris paribus, proportional to the number of elements it contains.

It is not absolutely necessary that the various pairs of elements composing a battery, provided they be kept moistened and separated, should be immersed in separate cells. The well-known battery, called the Voltaic pile, consisted of discs of zinc and copper, separated by discs of wet cloth. The battery, known as Pulvermacher's chain, is composed of cylinders of zinc enclosed in links of copper ; and when the various elements composing such a chain are moistened with an exciting fluid, such as vinegar, a current is generated having an intensity proportional to the length of the chain.

These simple arrangements are not capable of furnishing a constant supply of electricity, and batteries composed of such elements are liable to a rapid decrease of power from the moment of their being set in action. From this cause such batteries are of little use for medical purposes.

The cause of this decrease of power is evident. The dilute sulphuric acid tends to form sulphate of zinc, at the expense of the zinc plate, and thus the acid liquid becomes every moment less and less acid, and less and less capable of exerting any action upon the zinc plate.

A second and more important and powerful cause for the diminution of the current is the so-called polarization of the copper plate. It is well known that one of the results of the action of dilute sulphuric acid upon zinc is the generation of hydrogen, and part of the hydrogen so generated is deposited as a film upon the surface of the copper plate. This film of hydrogen offers great resistance to the passage of the current, and reducing the sulphate of zinc in solution causes a deposit of metallic zinc upon the copper plate, thus tending to destroy the current by bringing about a similarity between the two plates (the current, as we have said above, depending on the difference between them).

This defect has been almost entirely overcome by the invention of elements, which are capable, for a considerable length of time, of giving a constant current of electricity.

Daniell's constant element consists of two liquids and two metals. The copper is immersed in dilute sulphuric acid, which is saturated with sulphate of copper, and is separated from the simple dilute sulphuric acid, in which the zinc is immersed, by means of a vessel of porous earthenware.

The hydrogen liberated in the zinc-acid chamber traverses the wall of the porous vessel, reduces the sulphate of copper, and causes a deposit of metallic copper on the copper plate ; and the sulphuric acid liberated from the copper solution passing through the porous vessel helps to keep up the strength of the acid on the other side of it. The elements known as the Becker-Muirhead elements, which have attained a considerable reputation in this country both for medical and telegraphic purposes, and also those known as the Siemens- Halske elements, which are largely used for medical purposes on the Continent, are both of them modifications of the Daniell element.

Other well-known constant elements are those of Grove and the modification of them known as Bunseu's elements. In Grove's element we have two metals, platinum and zinc and two fluids, strong nitric acid and dilute sulphuric acid. The platinum, immersed in strong nitric acid, is separated from the zinc and dilute sulphuric acid by means of a vessel of porous earthenware. In this element the hydroo-en liberated in the zinc chamber traverses the porous vessel, and combining with some of the oxygen in the nitric acid, causes the escape of fumes of nitrous acid.

Bunsen's battery is, in principle, exactly similar to Grove's, the plate of platinum being merely superseded by a rod of compact gas-carbon (the carbon extracted from the retorts of the gas-works). This substitution of gas-carbon for platinum lessens the initial cost ; but the carbon has the disadvantage of being very brittle and liable to break at slight causes.

Grove's and Bunsen's batteries are not employed for medical purposes, excepting in those cases where a powerful current is needed for a short time, as during the employment of the galvanic cautery and the galvanic ecraseur.

Modifications of Bunsen and Grove are abundantly used for medical purposes. The modified Bunsen consists of plates of gas-carbon and zinc immersed, both of them in one liquid, dilute sulphuric acid.

This form of element is employed in the medical batteries manufactured by Dr. Stohrer, of Dresden, and by Messrs. Mayer and Meltzer, and others in this country. The carbon may be replaced by plates of silver, roughened on the surface by a deposit of finely divided platinum, which seems to prevent the adhesion of the hydrogen to the surface of the collecting plate. This is known as Smee's element, and is employed in the medical batteries manufactured by Messrs. Weiss. Another well-known modification of Bunsen's element is that employed in Stohrer's induction apparatus. The carbon is moulded into the form of a hollow vessel, whichis filled with sand moistened with chromic acid. In this element the hydrogen, passing through the porous carbon vessel, reduces the chromic acid.

An element largely employed for induction apparatus is known as Grenet's element, and consists of a zinc and a carbon plate, both immersed in the same liquid, a solution of bichromate of potash, to which a certain proportion of strong sulphuric acid has been added. In this element the hydrogen reduces the chromic acid to chromic oxide, which remains dissolved in the sulphuric acid.

Duchenne speaks very highly of the batteries which he has employed, composed of elements which we owe to the ingenuity of M. Marie- Davy. They may be called the sulphate of mercury battery and the sulphate of lead battery. In the first a rod of gas-carbon is packed in a porous cell with a paste made of sulphate of mercury. The porous cell is surrounded by a zinc cylinder which is immersed in pure water. In the sulphate of lead battery the sulphate of mercury is replaced by a paste made of sulphate of lead and a solution of sea salt. The carbon is replaced by a thin plate of copper and the pure water in the containing vessel by a solution of sea salt. The last is the cheaper element of the two, and it is stated that the current derived from it remains constant for many months.

The smallest element which has been introduced into medical practice is Gaiffe's chloride of silver element, consisting of a plate of zinc and a plate of compressed chloride of silver, separated by a pad of bibulous paper moistened with salt and water.

The element which at present deservedly holds the first place in public estimation is the Leclanche element, and there can be little doubt that it is destined to replace all other forms of element which have hitherto been used for medical purposes. This element is patent, the right of manufacture in this country being held by the India Rubber and Telegraph Company (Limited), but it can be obtained through any instrument maker. It consists of zinc and gas-carbon. The gas-carbon is packed in a porous cell with coarsely-powdered gas-carbon and native peroxide of manganese (pyrolusite). This poi-ous cell is placed in an outer vessel, containing a rod of zinc and a saturated solution of chloride of ammonium. The chemical action which takes place is as follows : — Chloride of zinc is formed and hydrogen and ammonia are set free. The ammonia is absorbed by the water in the outer vessel, while the hydrogen, passing through the porous cell, reduces the peroxide of manganese. The Leclanche element can be obtained of any size, those for medical use being of about the capacity of two-

PRINCIPLES.

10 PEINCIPLES.

ounce bottles. They are very strong ; the fluid in them cannot be spilt by any movement short of actual inversion ; they are little liable to get out of order, and remain almost absolutely constant for two or more years at a time. M. Tripier says : — ' For the last four years I have almost abandoned the protosulphate of mercury pile for the Leclanche element. . . . These couples, which cause no sensible waste when the circuit is open, work, for medical use, many years, without requiring any attention. . . . Having tried all the piles that have been proposed, I have stopped at this last, which I have employed for induction apparatus and for stationary galvanic batteries.'

The author is certainly inclined to the same opinion as M. Tripier. In February, 1874, he purchased a Leclanche element for the purposes of demonstration and experiment. After being used for the author's lectures at Charing Cross Hospital, it was put away in a cupboard and forgotten. Nine months later it was found, covered with dust and the solution of chloride of ammonium in the outer vessel, evaporated almost to dryness. On testing it, however, it was found to furnish a sufficient current to work an induction coil, and at present (July, 1875), after eighteen months of neglect, it is apparently as active as on the day it was bought.

Owing to the impurities of commercial zinc and its impregnation with particles of other metals, local galvanic action is liable to be set up at the zinc plate, causing its rapid destruction, even when the circuit of the battery is not closed. To obviate this, the zincs are usually amalgamated on the surface with mercury, which is found partially to arrest the local action. If sulphate of mercury be added to the acid liquid in which the zinc is immersed, metallic mercury is deposited upon the zinc plate, and thus the amalgamation is maintained.

All elements containing zinc and dilute acid are, however, exceedingly wasteful, even when the circuit is open. The practice of amalgamating the surface of the zincs with mercury is only partially successful in stopping the local action, which is constantly going on whenever the zincs are immersed in the acid. In consequence of this constant waste, it has been necessary to furnish all batteries having zinc and acid elements with a special mechanism for liberating the elements from the acid, whenever the battery is not required for use. In the Leclanche element, however, there is no wasteful action when the circuit is open ; and it is not the least advantage of employing this element that the mechanism above-mentioned is unnecessary ; and thus we gain in simplicity and save in cost, bulk and weight. On comparing a battery of sixty ' Smee ' elements with a Leclanche battery of fifty elements, it appears that, while the former occupies a cubic space of 1,696 cubic inches and weighs 42 lbs., the latter occupies a space of 714 cubic inches and weighs only 25 lbs. The fact that the Leclanche element is patent has, perhaps, somewhat hindered its adoption by manufacturers of batteries ; but Messrs. Weiss, whose reputa tion for perfection of mechanical detail and workmanship in the matter of batteries is so deservedly high, have at length united the Leclanche element to their own accessories, and the result cannot fail to be satisfactory. In using a Leclanche battery one caution is necessary, viz., never to leave the poles of the battery in metallic contact, i.e., united by a wire. If this accident should happen the battery would ' run down ' in a few hours.

These details concerning the various elements may have proved wearisome ; but a knowledge of their construction is absolutely necessary. The most perfect batteries are liable to strike woi-k at slight causes ; and without some knowledge of the construction of the elements and the chemical changes which take place in the cells, the practitioner will often find himself in difficulties, and will, perhaps, be sending his battery to the manufacturers for repairs which he might effect himself in a few minutes.

When a number of elements are united together in a series to form a battery, the generating plate of one element is put in connection with the collecting plate of the next, and so on, eAd the first generating plate and the last collecting plate of the series are united by a good conductor. When the two terminals are united by tbe conductor the circuit is said to be closed, and electrical action takes place. When they are not so united the circuit is said to be open, and electrical action ceases.

We have said that the various elements and the terminals must be united by a good conductor, and this brings us to speak of conductors and of non-conductors.

There are certain bodies which electricity traverses with greater or less ease — such are the metals, charcoal, acid liquids, and the animal body — and these are called conductors. There are, again, certain bodies which electricity traverses with the greatest difficulty — such as resins, gutta-percha, baked wood, and porcelain — and these are called non-conductors or insulators, because, when a conductor, charged with electricity, is surrounded by a non-conductor, the electricity with which the conductor is charged cannot escape, or, in other words, it is insulated.

There is, however, no conductor so perfect but that it offers some resistance to the passage of the current. Conductors differ enormously — caderis "paribus — in the resistance which they oppose to the current. The metals are the best conductors, and the best of the metals in this respect are silver, copper, and gold. Hence it is that copper, from its cheapness and low resistance, is so largely employed in the manufacture of galvanic batteries and conductors. The resistance offered by the metals varies very much, and it has been found that the resistance offered by lead and mercury is respectively about ten times and fifty times as great as that offered by copper.

The resistance of the best conducting liquids is vastly greater than that of metals. In round numbers, the resistance of dilute sulphuric acid is a million times, and that of a solution of sulphate of copper is ten million times, greater than that of pure silver.

It is important to bear in mind that we have to do with a very bad conductor indeed — one whose resistance to the current has been spoken of as colossal — we mean the human body. In the last edition of Dr. Althaus' book will be found much interesting and instructive information on this point, but for the present we will merely content ourselves with saying that the resistance of the human body is infinitely great ; and the anthor may add that, not long since, the resistance of his own body was found to be more than twice as great as that of the Atlantic cable. The resistances of various bodies, metals, liquids, &c, have been measured and compared to certain fixed standards, and thus, what is known as the specific resistance of these bodies, has been determined and may be expressed in numbers.

Metals, liquids, and animal bodies have all their specific resistances ; those of the last being infinitely greater than those of the first, while liquids hold an intermediate position. With regard to liquids, we may add that the concentrated acids offer the least resistance, and distilled water the most. Dilute acids and saline solutions hold an intermediate position.

While, then, electricity is traversing conductors, it is constantly encountering and overcoming resistances more or less great. The electricity generated at the zinc plate of a Daniell's element has, in making the circuit, to ovei'come the resistance offered, firstly, by the dilute sulphuric acid surrounding the zinc plate, which is considerable ; secondly, that offered by the solution of sulphate of copper, which is greater still ; thirdly, that offered by the copper plate ; and lastly, that of the copper wire, which unites the copper to the zinc plate again.

Now the resistance offered by a conductor depends not only upon the specific resistance of that conductor, but on other considerations as well. It will be obvious that a conductor a mile in length must offer a greater resistance than one a yard in length ; and such is found to be the fact, the resistance offered by the one being 1,760 times that of the other. In other words, the resistance offered by a conductor is directly proportionate to its length. A long stretch of liquid, wire, or animal tissue offers a resistance in exact proportion to its length.

Again, resistance is found to be influenced by another point, and that is, the area of the cross-section of the conductor. A wire of big calibre conducts better than one of small calibre, or, in other words, the resistance offered is in an inverse proportion to the area of the cut section. Electricity may be compared to water in a pipe, which necessarily traverses a short pipe of large diameter much easier than it traverses a long pipe of small diameter. A battery constructed for the galvanic cautery, and one designed for ordinary therapeutic purposes, offer very different amounts of resistance to the current. In the one, which is probably a large Grove's battery, we find that the plates used are very large and thin, or, in other words, they have a short length and enormous transverse section. Again, we find that the plates are as closely approximated as possible, so that we have in the conducting liquids the same conditions as in the conducting plates, viz., short length and enormous transverse section. Again, the liquids employed are both good conductors, one being a dilute acid and the other a strong acid. Further, the conducting- wire is short and of large diameter. In this arrangement the resistance is everywhere at a minimum, and, consequently, the quantity of electricity evolved is enormous. In the other arrangement (a Smee, for example) we have smaller plates, more widely separated in proportion to their size ; one liquid, which offers a moderate resistance ; and longer conductors, which when in use include a greater or less amount of the human body.

In speaking of resistances, we have to distinguish between the resistance offered by the battery itself, which is called intra-batterial or internal resistance, and that offered by the circuit outside the battery, which is called extra-bat terial or external resistance.

We must now ask the reader once more to turn his attention to the different varieties of elements which we have enumerated. These have not all the same electric power, or, as it is more properly called, the same electro-motive force. Those elements in which the greatest amount of chemical action takes place have the greatest electro-motive force — the greatest power of generating and propelling, as it were, the electricity originating in them. The electro-motive force of a Grove or Bunsen is greater than that of a Daniell or Smee. Taking the electro- motive force of a Grove as 100, that of a Bunsen is said to be 98, and that of a Daniell only 56. The electromotive force of a Smee is, again, scarcely half that of a Daniell, while the electro-motive force of the Leclanche element is slightly in excess of the Daniell's element.

The amount of attention which a battery requires is usually in direct proportion to its electro-motive force, so that, for this reason as well as others, the practical physician uses for general purposes elements of low electro-motor power, such as Leclanche, Daniell, Smee, or Stohrer.

That which is called the Intensity of an electric current depends upon the quantity of electricity which in an unit of time flows through a section of the circuit, and in all parts of the circuit the intensity is always uniform.

We are now in a position to consider Ohm's law, a right understanding of which is indispensable for the satisfactory study of electro-therapeutics. Ohm's law is to this effect, that the intensity of a current is equal to the electro-motive force divided by the resistance ; or

E I= E

Now we have pointed out that the resistance offered to a current is of two kinds, intra-batterial and extra-batterial. If we designate the one by R and the other by r, then our formula becomes

_ E

Ifi PRINCIPLES.

Supposing we multiply the number of our elements-say by 6— then the formula becomes

6e .

I== 6E+r ' for by increasing the number of elements we increase the intra-batterial resistance. The result of such multiplication of elements will be different according to the value of r— the extra-batterial resistance. Let us suppose that the value of r i's practically 0, as is often the case when the circuit of a battery is completed by a metallic conductor of large calibre, then r may be neglected and our equation becomes

Thus the intensity of the current, in the case we have sup. posed, has remained the same after the multiplication of the elements. Hence arises the law that —

' When the resistance of the circuit is insignificant in comparison with the resistance of the element, the intensity of the current is not increased by the multiplication of the elements.'

Next, let us suppose that the intra-batterial resistance is insignificant when compared with the extra-batterial, then R becomes a quantity which we may neglect, and our equation

becomes i=-^i-=— . In this case by multiplying our ele-

0+r r ments by 6 we have increased the intensity of our current 6 times, or nearly so.

Hence the next rule is —

' When the resistance of the element is insignificant in comparison with that of the circuit, the intensity of the current increases proportionally to the number of the elements.'