251
`
`Stiiniilatioti of Prritable Tissues by Means oC an Alternating Magnetic Field.*
`( 2 m 9 )
`
`(Introduced by I,. LV. Roth)
`Uepi . of Biophysics, Univrrsity of California, Los Angeles
`
`A u c x A N m x ~ U L I N , NORMAN 0. Ritii.1, A N D I’AU~, 1. HROBEKG
`
`Observation of visual sensations not caused
`by light, by technicians working in the vici-
`nity of large choke coils carrying strong alter-
`nating currents, was reported by Thompson
`( 1). He was able to reproduce such an effect
`by exposing the head of human subjects to an
`extensive a1 ternating magnetic field generated
`inside a large coil. This phenomenon (“phos-
`phenes”) has also been studied by others( 2-5).
`The stimulation is evidently due to eddy cur-
`rents induced in the tissues exposed to the al-
`ternating magnetic field. No attempt has
`been made in any of these investigations to
`localize the stimulus. The nearest approach
`to a search for local effects of ,an alternating
`magnetic field was an attempt by Magpusson
`and Stevens(4) to stimulate a (cat’s nerve by
`disposing it transversely
`in a.n a1 ternating
`magnetic field. The result of this experiment
`was negative.
`Methods. The magnetic fields used in the
`above-mentioned experiments were obtained
`with electromagnets excited with low fre-
`quency a.c. (below 90 cps) as well as with in-
`termittent d.c. The observed light sensation
`was monochromatic (bluish white) ? flickering
`and strongest near the periphery of the retina.
`To obtain a more nearly localized effect in
`our experiments, a bar electrornagnet with a
`pyramidal pole tip, shown in Fig. 1, was con-
`structed. Distribution of the axial field in-
`tensity component is shown in the same dia-
`gram. Currents of 2 frequencies have been
`used to energize this magnet, 60 cps and 1,000
`cps. The maximum flux density obtained at
`the pole tip with the 60 cps source (a.c. line
`voltage) was 8,740 gauss (rms) and with the
`1.000 cps source (motor-generator set), 2,2 60
`gauss (rms) . In spite of the lower flux den-
`sity at 1,0001 cps, the induced eddy currents
`are stronger as compared to those induced at
`60 cps due to the proportionality of the in-
`* This work supported by grant from Office csf
`
`Naval Research.
`
`duced e.m.f. to rate of change of the magnetic
`field.
`Results. Observations of the phosphenes
`reported by previous authors have been veri-
`fied a t 60 cps. The flickering light sensation
`was strongest when the pole tip was held
`against the temporal area but could still be de-
`tected when the pole was placed against the
`occipital area. No other sensations or effects
`were observed in varying the location of the
`pole tip relative to different areas of the cor-
`tex.
`At 1,000 cps a new effect was observed
`when the magnet pole was close to the tem-
`ple. There was an intense sensation of nasal
`obstruction experienced by all subjects.
`It proved possible to stimulate frog nerves
`intensely at 60 cps as well as a t 1,000 cps by
`winding a nerve about the pole tip to form a
`closed one-turn bop. The pole tip was well
`insulated by a cap of acrylic plastic material
`(“Densoform”). A nerve-muscle preparation
`of a frog’s sciatic nerve attached to the gas-
`trocnemius muscle was used (Fig. 1 ) . Tn-
`tense tetanic contractions of the muscle were
`obtained whenever the magnet was excited.
`Fig. 2 shows a record of the muscle contrac-
`tion with a simultaneous recording of the pat-
`tern of the stimulus. The latter recording was
`obtained by registration of the e.m.f. induced
`by the stimulating magnetic field in a loop
`surrounding the pole tip. The same effect
`has also been obtained in a substantially ho-
`mogeneous 60 cps magnetic field of 6,000
`gauss rms flux density. f t also proved pos-
`sible to stimulate contraction in excised frog
`muscles placed in a Petri dish and submerged
`in Ringer’s solution. The Petri dish was
`placed into the gap of an electromagnet gener-
`ating a 60 cps magnetic field in a 5 x 15 cm
`gap of 2.8 cm pole separation. The bottom
`of the Petri dish was parallel to the horizon-
`tally oriented poIe faces. Tetanic contractions
`olf freshly excised muscles were observed while
`
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`

`252
`
`STIMULATION OF IRRITABLE TISSUES
`
`the magnetic field was on. Stimulation of the
`irritable tissues by the eddy currents induced
`in the contents of the Petri dish showed a de-
`pendence on their position in the dish as well
`as on their orientation. The maximum effect
`was observed when the muscle was placed
`near the rim of the Petri dish and no effect
`was seen when the muscle was a t the center.
`With the muscle placed near the rim, the con-
`traction was strongest when the longitudinal
`axis of the muscle was oriented tangentially
`and least strong or absent for the radial orien-
`tation. These observations are in accordance
`with the anticipated distribution of eddy cur-
`rents which flow along the rim of the Petri
`
`Pu
`
`FIG. 1. EM: laminated bar electromagnet generating
`a non-homogeneous alternating magnetic field the
`axial component of which is represented in the dia-
`gram as a function of distance from the pole face P.
`N: nerve forming a closed loop in magnetic field.
`M: frog's gastrocnemius muscle. C: wire loop sur-
`rounding pole tip of the magnet. R: rectifier which
`rectifies the a.c. signal induced in loop C. The recti-
`fied signal is recorded by one of the 2 recorder chan-
`nels. PC: photocell (International Rectifier Corp.
`type B-10) of
`the photoelectric device recording
`muscle contraction. L: light source. S: shutter which
`can be lifted by the string attached to frog leg. The
`shutter is actually flush with bottom of photocell PC.
`It is represented somewhat longer in the diagram to
`show the point of attachment of the string to which
`weight W is attached. When muscle contracts, shut-
`ter S and weight W are lifted thus exposing an in-
`creasing area of the photovoltaic cell PC to light from
`the source L. Voltage output of photocell is recorded
`by the second channel of the 2-channel recorder.
`
`TIME
`t
`
`FIG, 2. Temporal relationship between stimulus and
`response in electromagnetic stimulation. A. Photo-
`electrically recorded movement of frog leg produced
`by contraction of the gastrocnemius muscle. Muscu-
`lar contraction is evoked by stimulation of the nerve
`S of Fig. 1 through the current induced in it by the
`alternating magnetic field. B. The stimulus as a func-
`tion of time in arbitrary units as represented by recti-
`fied and filtered e.m.f. induced in loop C of Fig. 1.
`
`dish. The stimulating action of alternating
`magnetic fields depends on the induced eddy
`current density. It is reasonable to assume
`that an increase in intensity and, to a limited
`extent, in frequency of the alternating mag-
`netic field used would lead to observation of
`effects which were not observed at the eddy
`current densities produced under the condi-
`tions described above.
`Summary. Stimulation of frog nerves and
`of excised frog muscles submerged in Ringer's
`solution has been obtained without the use
`of electrodes by means of sinusoidal alternat-
`ing magnetic fields. This effect is due to eddy
`currents induced in conductive tissues and
`their surroundings. Visual and non-visual
`sensations have been induced in human sub-
`jects by non-homogeneous alternating mag-
`netic fields adjacent to the brain.
`The authors are indebted to Mr. R. T. Kado
`for valuable technical assistance.
`
`1. Thompson, S. P., Proc. R o y . Soc. B, 1910, v82,
`.196.
`2. D'Arsonval, M. A., C. R. Biol., Paris, 1896,
`v48, 450.
`3. Dunlap, K., Science, 1911, v33, 68.
`
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`

`CATIONS AND CANINE TAG
`
`2 53
`
`4. Magnusson, C. E., Stevens, H. C., Am. J .
`Physiol., 1911, v29, 124.
`5 . Barlow, H. B., Kohn, H. I., Walsh, E. G., ibid., Received July 16, 1959.
`
`1946, ~ 1 4 8 , 3'12.
`
`P.S.E.B.M., 1959, V102.
`
`Cation Specificity of Thrombocyte Agglutinating Activity ( T A g ) of C a n i n e
`(25210)
`Plasma.*
`R. G. MASON,+ E. C. LEROY~ AND K. RI. BRINXHOUS
`Dept. of Pathology, University of N o r t h Carolina, Chapel Hill
`
`Canine plasma possesses the ability to ag-
`glutinate homologous and autologous platelets
`rapidly in the presence of Mg++ or &In++ (1).
`This property of plasma has been termed
`thrombocyte agglutinating activity (TAg) .
`TAg is contained in crude gNobulin fractions
`of plasma, but not in the albumin fractions.
`I t is non-dialyzable and heat-labile. TAg ap-
`pears to be separate from the plasma proco-
`agulants, fibrinogen and antihemophilic fac-
`tor, as well as from prothrombin and related
`BaS04-adsorbable factors. In this study TAg
`was tested for activity with 15 separate ca-
`tions. The active ions were studied further to
`determine the relative amounts needed for
`prompt agglutination of platelets with TAg.
`Methods. Details of the macroscopic plate-
`let agglutination test for TAg have been de-
`scribed( 1 ) . The test is done in 2 stages. In
`the first or incubation stage, canine plasma is
`incubated for 30 min. with a cation chloride
`solution. In the second or agglutination stage,
`a standard suspension of washed canine plate-
`lets is added to the incubation mixture and
`time and degree of agglutination determined.
`Three types of canine plasma were used.
`Resin plasma was prepared by use of Dowex
`50 resin columns( 1). Oxatate plasma has
`been described(2). EDTA plasma was pre-
`pared by mixing 9 parts of whole dog blood
`with one part of stock EDlTA solution( l ) ,
`previously diluted one to' 3.27 with normal
`saline. Plasma dialysis against 0.154 M NaCl
`was carried out with Visking casing (18 hr
`continuous agitation, 4°C). Adsorbed plas-
`mas (resin, oualate, or EDTA) were prepared
`* This investigation was suppcrted in part by
`grant from Nat. Heart Inst., N.J.H., P.H.S.
`t Post-Sophomore Research Fellow, N.I.H., P.H.S.
`
`by adding to' each ml plasma 100 mg Bas04
`(Merck) (contact time 30 min, 4°C) and re-
`peating the procedure once. In the prothrom-
`bin time test with adsorbed plasmas no clot
`formed in 10 min. The chloride salts of vari-
`ous cations were used; all salts were Baker
`A.R., except FeC13 (Mallincrodt) , PbCb
`(Fisher), and BaC12 (Merck) . Solutions
`were standardized by chloride analyses,
`and diluted to 0.108 M. For weaker so-
`lutions, serial 2-fold dilutions were made
`with 0.154 M NaC1. Cation concentration
`in
`the experiments
`is expressed as mM
`cation added per liter of plasma incubation
`mixture. Platelet suspensions( 1) were pre-
`pared from EDTA canine plasma and con-
`In several ex-
`tained 4 * lo5 platelets/cmm.
`periments, platelet preparation was modified
`by resuspending the platelets in solutions con-
`(Armour).
`taining 0.5% bovine albumin
`With this modification the platelet pellet could
`be resuspended rapidly, and platelet reactiv-
`ity was unchanged.
`TAg and B a S 0 4 adsorption of
`Results.
`plasma. A series of tests were performed to
`determine the effect of BaS04 adsorption of
`plasma on platelet agglutination by TAg. Fig.
`1 shows the results obtained with resin plasma
`before and after adsorption, With either Mgi+
`or Mn '+, rapid agglutination occurred, regard-
`less of plasma adsorption or cation concentra-
`tion used. Only with adsorbed plasma a t the
`lower A h + + concentrations were agglutination
`times less rapid
`than with non-adsorbed
`plasma. With Ca++, on the other hand, no
`agglutination occurred with adsorbed plasma;
`with non-adsorbed plasma, clotting occurred
`in the incubation phase and the resultant se-
`rum caused moderately rapid agglutination.
`
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