Effects of intraluminal nutrients on intestinal ...

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and by phenoxybenzamine on the ileum. We conclude that the initial excitatory phase induced by luminal amino acids and sugars may be dependent on an ...
Effects of intraluminal nutrients myoelectric activity in rabbits THIERRY Department

BOUYSSOU,

of Physiology, Y

MICHEL

PAIRET,

Ecole Nationale

(Gastrointest. Liver Physiol. 18) GE-G17, 1988,--In the unanesthetized rabbit, intraluminal infusions of D- and L-methionine, L-tryptophan, D-&cOSe, D-xylose, and lactulose had a biphasiceffect on smallintestinal myoelectric activity. A phase of enhancedactivity wasfollowed by a phaseof inhibition. The excitatory phasewas mimicked by saline solutionsequiosmolar to the test-solutions. The subsequentinhibition was dosedependent and significantly (P < 0.01) longer for the passively absorbedD-methionine than for the L-stereoisomer.The inhibitory action of IO mM D-glUCoSe, 10 mM L-methionine, and 5 mM L-tryptophan was blocked by propranolol on the jejunum and by phenoxybenzamine on the ileum. We conclude that the initial excitatory phase induced by luminal amino acids and sugars may be dependent on an action on osmoreceptors, whereasthe subsequentinhibitory phasemay involve the sympathetic noradrenergic system. intraluminal infusion; noradrenergic system; osmoreceptors

EFFECTS on small intestinal motility of intraluminally administered nutrients such as amino acids and glucose have been studied in the conscious fasted dog (1, 3) and rat (11) A phase of irregular spiking activity similar to the effect of feeding was provoked. It was concluded that the local actio.n of nutrients may be in part responsible for the myoelectric response to a meal of the small intestine, i.e., the migrating motor complex (MMC) is disrupted and replaced by irregular activity (2, 8, 14). In herbivores, such as ruminants and rabbits, the fasting small intestinal myoelectric activity is similar to the MMC of the fasted dog but is not disrupted by a meal when these animals are fed ad libitum (10,lZ). The effects of nutrients on small intestinal motility may thus be different in omnivores and herbivores. So we thought it would be of interest to study the effects of intraluminal infusions of methionine, tryptophan, glucose, xylose, and lactulose on rabbit small intestine myoelectric activity. The relationship between intestinal absorption and motility has been studied by different authors. Absorption of glucose, electrolytes, and water is usually increased when the level of intestinal motility is low and vice versa. Accordingly, absorption of water and electrolytes is facilitated and the intestinal motility is reduced under the influence of the sympathetic nervous system in most species, including the rabbit (13). Another aim of this study, then is to assess the role of the sympathetic THE

G12

019%1857/M

$1.50 Copyright

MICHEL

Wtkrinaire,

BOUYSSOU, THIERRY, MICHEL PAIRET, MICHEL CANDAU, AND YVES RUCKEFNJSCH. Effects of intrakuminal nutrients on intestinal myoelectric activity in rabbits. Am. J. Physiol. 255

on intestinal

CANDAU,

AND

31076 Toulouse C&x,

YVES

RUCKEBUSCH

France

nervous system in the myoelectric changes induced by intraluminal infusions of sugars and amino acids into the jejunum of rabbit. MATERIALS

AND

METHQDS

Animal Preparation

California male rabbits, 55-70 days old, weighing 1.5 2 kg, and receiving a diet containing 16% cellulose and 15% crude protein ad libitum, were used. Fasted rabbits were anesthetized with thiopental sodium (Nesdonal Sodium, 20 mg/kg) administered through an ear vein (iv), and surgery was performed using aseptic precautions. The small intestine was reached through a midline abdominal incision, and three groups of three insulated nichrome electrodes (0.08 mm diam, Trinamel, Johnson Matthey, London, UK) were implanted, as previously described (9). The exact sites were the following: on the duodenum, 30 cm distal to the pylorus (P + 30); on the distal jejunum, 40 cm proximal to the ileocecal valve (ICV - 40); and on the ileum, 5 cm proximal to the ileocecal valve (ICV - 5). Each rabbit was fitted with a silicone open-tipped catheter (2 mm OD) 45 cm proximal to the ileocecal valve (ICV - 45). Figure 1 represents the location of the catheter and electrodes along the rabbit small intestine. The free ends of the catheter and electrodes were brought subcutaneously and exteriorized on the back of the neck. Experimental Procedure

Recording began 5-9 days after surgery, when the rabbits were consuming X20 g of feed daily. Recording sessions lasted 10 h (0900-1900 h) and took place every 48 h. During each session the animals were restrained in a rabbit box to prevent feeding and cecotrophy. The electromyogram was recorded continuously using an electroencephalograph (Reega VIII, Alvar, Paris) with a time constant of 0.1 s. The spiking activity was automatically plotted by means of a four-channel integrator (7) connected to a potentiometric recorder (PM 8010, Philips, Bobigny), and quantified using an Apple IIe with an eight-channel analog-to-digital converter (Progetec ADC 8 B 100 M) (8). The numerical values were obtained for each lo-min recording epoch during 10-h periods. The control myoelectric activity index was calculated as the mean value of the first two lo-min recording periods that preceded the infusion of each substance. This value was considered

0 1988 the American

Physiological

Society

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INTRALUMINAL

NUTRIENTS

AND MYOELECTRIC

FIG. 1. Schematic diagram of rabbit small intestine with position of electrodes (L-3) and catheter (C). b, Bile duct; d, duodenum; P, pancreatic duct; J, jejunum; I, ileum; Ce, cecum; Co, colon.

as 100, and the level of myoelectric activity during the infusion was expressed as a percentage of the control index. When a change in myoelectric activity was observed during the postinfusion period, its duration was determined as the number (n) of lo-min recording pe-

Data Analysis The level of myoelectric activity during the infusion and postinfusion periods was expressed as a percentage of the control index for each rabbit and as the means & SE for the grouped data. The duration of the postinfusion inhibitory period was expressed as the mean of the individual values. No SE or

of

the control values; the mean myoelectric index was then calculated for these n periods for the test solution and Duodenum

P + 30

G13

the equiosmolar saline solution. The test and control solutions (NaCl) were dissolved in 30 ml of distilled water and buffered to pH 7 (with 0.2-0.4 ml NaOH 0.1 N). They were injected via the jejunal catheter over a period of 30 min at a rate of 1 ml. kg-‘.rnin-‘. The infusion took place during the irregular spiking activity (ISA) phase of an MMC on the jejunum; only one infusion was performed during each recording session. Eight rabbits received 1,5, and 10 mmol L-methionine, 1 and 5 mmol D-methionine, and 5 mmol L-tryptophan as well as the control saline solutions, in a random order. Eight other rabbits received 5 and 10 mmol D-glucose, 10 mmol D-~ylose, 10 and 20 mmol lactulose, and the control solutions. Finally, eight other rabbits received 10 mmol D-glucose, 10 mmol L-methionine, and 5 mmol Ltryptophan after a previous intravenous injection of either placebo, the a-blocker phenoxybenzamine (PBZ, 1 mg/kg), or the ,&blocker propranolol (PPL, 1 mg/kg). The osmolality of each test solution (amino acid or sugar) was measured by freezing point depression. The theoretical concentrations of the control saline solutions for osmolality were calculated and prepared; the osmolality of each saline solution was then measured by freezing depression”

C

riods during which the myoelectric index was 40%

ACTIVITY

cm

16 I”C Jejunum

ICV

-4Ocm

* FIG. 2. Integrated record of intestinal myoelectric activity in rabbit at duodenal (electrode site I) and jejuno-ileal levels (electrode sites 2 and 3). Note t,hat full scale (16 PC) is reached during a phase of maximal spiking activity, the regular spike activity phase (*).

?

I

hour

I

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G14

INTRAI.

Duodenum

Jejunum

NUTRIENTS

LJMINAI

AND

MYOELECTRIC

ACTIVITY

mg/kg D-xylose were given intravenously. This dosage is thought to produce similar blood concentrations as those reached when 10 mmol D-xylOSe was intraluminally infused. Blood samples were collected from an ear vein 15 min after intravenous injection of D-xyhm, and plasma D-XY~OS~ concentrations were determined by calorimetry using phloroglucinol (3).

P + 30cm

I CV, -4Ocm

RESULTS

Patterns of Myoelectric Activity I leum

The electrical activity of the rabbit small intestine consisted of slow waves and superimposed spike bursts. Spike bursts were irregularly superimposed on slow waves on the duodenum. On the jejunum and ileum, the myoelectric activity was organized into migrating myoelectric complexes (12) with the characteristic three phases: phase 2 or ISA, phase 3 or regular spiking activity (RSA), and phase 1 or quiescence, with no spiking activity (NSA) (Fig. 2).

I.C.V. - 5 cm

L MET FIG.

3. Effect

,

IOmrnoL

of a lo-mmol

infusion

I hour

of L-methionine

(MET)

(

on

integrated myoelectric activity of rabbit small intestine. A phase of intense spiking activity is recorded and coincides with duration of infusion. Then follows a marked inhibition of lOO- to HO-min duration. Note that during this phase of inhibition, regular spike activity phase (*) of an migrating motor complex is not altered.

sem were calculated because of the discontinuity of these individual values (determined from 1 to 10 min). Statistical analyses were performed using the distribution free Wilcoxon paired t test. Ancillary

Experiments

Blood D-xylose concentration measurement. In the rabbits that received 10 mmol D-xyh?, 2-ml blood samples were collected from an ear vein 15 min after the end of the infusion. Plasma D-xylose concentrations were determined by calorimetry using phloroglucinol (3). Intravenous injection of D-xylose. In three rabbits, 8 TABLE

Effects of Jejunal Infusions of Amino Acids and Sugars r;-Methionine. A l-mmol infusion of L-methionine had no effect on the rabbit intestinal myoelectric activity. Administration of 5 and 10 mmol induced an increase in electrical activity during the time of infusion. This was followed by a marked dose-related inhibition of the activity of the jejunum and ileum (Fig. 3). The increase in activity but not the subsequent inhibition was mimicked by equiosmolar control solutions (Table 1). D-Methionine. One- and five-millimolar infusions of D-methionine also induced a biphasic response on the jejunum and ileum. The phase of increased activity, lasting the time of the infusion (Table l), was followed by a marked dose-related inhibition. L-Tryptophan. A 5-mmol infusion of L-tryptophan induced a period of increased spiking activity, followed by an inhibition of the jejunum for 40 min and of the ileum for 80 min (Table I).

1. Effects of jejunal infusions of amino acids on small intestinal spiking activity in rabbits Stimulation

Infusion Substance

Osmolality, mosmol/kg

Myoelectric Duodenum

L-Methionine (5 mmol) L-Methionine (10 mmol) D-Methionine (1 mmol) D-Methionine (5 mmol) L-Tryptophan (5 mmol) Saline

Inhibition Myoelectric

index Duodenum

Jejunum

index

Duration,

Jejunum

Ileum

130

98t7

142t7*

128t5*

91t6

43*6*-j-

35-+7*

255

89t5

153tl2*

147t6’

1093-5

23+5*t

26t5*

25

105t6

116zt8

110t9

102zk4

56+9*-f

43*10*

21-t

2w

130

93t3

138t5*

122t3*

86tll

21+7*“f

32t8*

gwz

125tS

50

97+4

144*7*

126t5*

108k8

42-+9*

41-t-6*

53

73

25 130 255

lOOt3 97t4 102t7

104t4 135t4* 159t6*

lOlt6 131-+5* 146t7*

99-t3 963-4 102t5

98k3

9424 97+11 llOk12

105t12 lllt6

Ileum

Jejunum

min

38-M 114t

Ileum

WS 159‘F

Values for myoelectric index are a percentage of control values during either stimulation or inhibition and are means t SE (n = 8). Values for duration of inhibition were estimated from 1 to 10 min and are means (72 = 8). * Significant with P < 0.01 when comparing with control (100%); “f significant with P < 0.01 when comparing 5-10 mmol L-methionine and l-5 mmol D-methionine; $ significant with P < 0.01 when comparing 5 mmol D- with L-methionine, Note that there is no significant difference during phase of stimulation when comparing test solutions to equiosmolar saline solutions and that response to saline solutions is dose dependent. Downloaded from www.physiology.org/journal/ajpgi by ${individualUser.givenNames} ${individualUser.surname} (148.188.001.060) on December 12, 2017. Copyright © 1988 American Physiological Society. All rights reserved.

INTRALUMINAL OUOOENUM

NUTRIENTS

16 /pc

JEJUNUM

G15

ACTIVITY

duce any change in rabbit small intestine myoelectric activity. Lactulose. A lo-mmol infusion of lactulose induced a phase of enhanced spiking activity on the jejunum and ileum, which was not followed by a phase of inhibition. When 20 mmol lactulose was infused, a postinfusion inhibitory period was observed that lasted from 20 to 50 min (Table 2).

P*3h~i

.

AND MYOELECTRIC

I.

Effects of Sympathetic Blockers on Myoelectric Changes Induced by Jejunal Infusions of Amino Acids and Sugars in Rabbits ILEUM

1.c.v.

The subsequent inhibitory effect of luminal infusions of 10 mmol D-ghCOSe, 10 mmol L-methionine, and 5 mmol L-tryptophan on the rabbit small intestine myoelectric activity was almost completely prevented by the ,&blocker propranolol on the jejunum and by the cyblocker phenoxybenzamine on the ileum (Table 3, Fig. 5), whereas the short-lasting stimulatory action persisted unchanged.

-

I hour

4

4. Effect of a 10 mmol infusion of D-glucose (DGLU) on integrated myoelectric activity of the rabbit small intestine. During phase of inhibition, regular spike activity phase (*) still occurs and propagates. FIG.

D-Glucose. A 5-mmol infusion of D-glucose induced either no effect (5 rabbits) or similar effects as those observed with the amino acids, i.e., stimulation and then inhibition. When observed, these effects were of small amplitude and short duration. With a IO-mmol infusion, these effects were marked enough to be significant, as indicated in Fig. 4 and Table 2. D-Xylose. A lo-mmol infusion of D-xylose induced, as observed with D-ghCOse, a phase of enhanced spiking activity followed by a phase of inhibition of 34 and 23 min on the jejunum and ileum, respectively (Table 2). DXylose concentration obtained from ear vein blood samples 15 min after the end of the infusion was 18 t 0.7 (SE) mg/lOO ml plasma. An intravenous injection of 8 mg/kg D-xybe, which produced blood concentrations of 16 t 1.7 mg/lOO ml, allowed us to verify, in three rabbits, that plasma Dxylose concentrations similar to those reached when 10 mmol D-xylose was intraluminally infused, do not pro-

DISCUSSION

When amino acids and sugars were infused via the jejunal catheter, a biphasic response was recorded on both the jejunum and the ileum distal to the site of infusion. This response was a short-lasting phase of increased activity followed by a long-lasting phase of inhibition. In the dog and the rat, the response is different and limited to a phase of increased activity only (1, 4)) suggesting species-related differences. If we postulate that the local action of nutrients partly responsible for the myselectric response of the small intestine to a meal is species related, a different response from that in dogs and rats in the rabbit is understandable. Another factor could be the experimental procedure. In the dog and rat experiments, the infusions were performed in the quiescent phase of an MMC, when a phase of increased activity is easier to detect, and an inhibitory phase cannot be observed. In our experiments, the infusions performed during the ISA phase of an MMC facilitated the detection of a phase of inhibition. The myoelectric changes induced by intraluminal amino acids and sugars may be linked to either the

2. Effects of jejunal infusions of D-glucose, D-xylose, and lactulose on small intestinal spiking activity in rabbits TABLE

Stimulation Infusion Substance

D-Glucose (10 mmol) D-Xylose (10 mmol) Lactulose (10 mmol) Lactulose (20 mmol) Saline

Qsmolality, mosmol/kg

Myoelectric

Inhibition index

Myoelectric

Duodenum

Jejunum

Ileum

376 432 383

103t5 10524 10424

165&7* 156tll* 155&10*

149+9* 143t6* 143&g*

712

103t5

400 720

93&3 97t4

index

Duodenum

Jejunum

Ileum

105t5 99t6 102t5

35t6* 41t10* 104t8

35t6” 54t14* 103t9

178t12*

17ot,10*

10024

32tlO*

158t8*

160*12* 164tll*

105t4 10225

99t5 98t8

172t9”

-

41t12*

Duration, Jejunum

min Ileum

41 34

34 23

40

30

98t3 10526

Values for myoelectric index are a percentage of control values during either stimulation or inhibition and are means t SE (n = 8). Values with P < 0.01 when compared with control for duration of inhibition were estimated from 1 to 10 min and are means (n = 8). * Significant (100%). Downloaded from www.physiology.org/journal/ajpgi by ${individualUser.givenNames} ${individualUser.surname} (148.188.001.060) on December 12, 2017. Copyright © 1988 American Physiological Society. All rights reserved.

INTRALUMINAL

Gl6

NUTRIENTS

AND MYOELECTRIC

ACTIVITY

3. Effects of sympathetic blockers on the duration of inhibition induced by amino acids and D-glucose on rabbit jejuno-ileum -1____.---~l_l---_~D-Glucose (10mmd) L-Methionine (10 mmol) TABLE

-_____--~L-Tryptophan

--

Control

PBZ

PPL

Control

PBZ

----

PPL

Control

(10 mmol) PBZ

PPL

Duration of inhibition, min 46 53 10* 48 55 14* 141 143 18* Jejunum 6* 43 136 9* 6* 63 Ileum 36 131 71 Values are means (72= 8). * Significant with P < 0.01 when comparing treatment with control. PBZ, phenoxybenzamine; PPL, propranolol.

JEJUNUM

I.C.V.

A

- 40cm

I

I LEUM

icv.

- Scm

L f?bt JEJUNUM

I.C.V.

L. MET. fOm mo1 Img /Kg. 1.V.

- 40cm

I hour

0

0

/

iL.EUM

I.C.V.

FIG. 5. Effects of phenoxybenzamine (PBZ; A) and propranolol (PPL; B) (1 mg/kg iv) on inhibitory action of 10 mmol L-methionine (MET) on rabbit small intestinal integrated myoelectric activity. PBZ blocks the postinfusion inhibitory phase on ileum but not on jejunum. Note persistence of regular spike activity phase during inhibitory period on jejunum. PPL blocks postinfusion inh’b’t 1 1 ory phase on jejunum but not on ileum.

-5cm

Lf?pL ImgdKgmol. I.V. L.MET.IO~

I hour

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INTRALUMINAL

NUTRIENTS

presence of the nutrients in the intestin .a1 lumen, their passage through the intes tinal wall (i.e., absorption), or their blood concentrations. The excitatory resbonse recorded exclusively during the infusion of the test and of the control solutions seems to be because of their presence in the intestinal lumen. The fact that the excitatory response of the rabbit small intestine to control saline solutions increased with the increase of the osmolality of these solutions and the fact that there was no difference when comparing the test solution to the equiosmolar saline solutions (Table 1) support the hypothesis of an activation of nonspecific osmoreceptors. The second inhibitory phase was recorded with almost all the test solutions but was never observed with the control saline solutions. This finding demonstrates that I) the inhibitory phase is not reflexly induced by the first excitatory phase and 2) it depends on the nature rather than on the osmolality of the perfusate. All the aminoacids and sugars that induced an inhibitory effect are known to be easily absorbed (6). No postinfusion inhibitory phase was recorded with IO mmol lactulose, which is known to be poorly absorbed. Furthermore, the D-stereoisomer of methionine, which is passively absorbed (15), induced an inhibition significantly longer than the actively absorbed L-isomer. These results may indicate that absorption plays a role in the postinfusion inhibitory phase. However, the fact that a high concentration (20 mmol) of lactulose induced a postinfusion inhibitory phase might indicate that absorption is not a necessary step for this effect; alternatively, one might speculate that in such a high amount lactulose is partially absorbed. Luminal disappearance studies are needed to further investigate this hypothesis. On the other hand, the intravenous injection of 8 mg/kg D-XylOSe that produced similar blood concentrations as those reached when 10 mmol D-XylOSe was intraluminally infused, did not evoke any myoelectric change. So, if absorption plays a role, it seems that the transport of substance through the enteric wall is involved rather than the provoked blood concentrations. The effects of intraluminally administered aminoacids and sugars may be mediated by a nervous pathway and/ or by the release of endocrine or paracrine hormones. Because the specific effect of the substances we administered was an inhibitory one and because the sympathetic nervous system is known to reduce intestinal motility in most species including the rabbit (13), we tested the role of the sympathetic nervous system in the postinfusion inhibitory phase. The fact that phenoxybenzamine almost completely blocked the inhibitory effects of 10 mmol D-&COSe, 10 mmol L-methionine, and 5 mmol L-tryptophan on the rabbit ileum demonstrates the participation of the cy-

AND

MYOELECTRIC

G17

ACTIVITY

component of the sympathetic system on this intestinal segment. Sympathetic ,&receptors seem to be involved in the inhibitory effects recorded on the jejunum, since these effects were blocked by propranolol. In conclusion, aminoacids and holoses, when injected intraluminally in the rabbit jejunum, induced a biphasic response that consisted of a phase of enhanced myoelectric activity followed by a sustained phase of inhibition. The first phase was dependent probably on the action on osmoreceptors, whereas the second involved the sympathetic noradrenergic system. Further studies are needed to clarify the role of absorption in this inhibitory phase. Received

28 January

1987; accepted

in final

form

9 February

1988.

REFERENCES 1. BULL, J. S., D. GRUNDY, AND T. SCRATCHERD. The effect of intraluminal tryptophan and phenylalanine on small intestinal motility in the conscious dog. J. PhysioZ. Lond. 367: 353-362, 1985. 2. CODE, C. F., AND J. A. MARLET*. The interdigestive myoelectric complex of the stomach and small bowel of dogs. J. Physiol. Lond. 246: 289-309,1975. 3. EBERT~, T. G., R. H. B. SAMPLE, M. R. GLICK, AND G. H. ELLIS. A simplified, calorimetric micromethod for xylose in serum or urine, with phloroglucinol. Clin. Chem. 25: 1440-1443, 1979. 4. EECKHOUT, C., I. DE WEVER, G. VANTRAPPEN, AND J. HELLEMANS. Local disorganization of the interdigestive Migrating Myoelectric Complex (MMC) by perfusion of a Thiry-Vella loop (Abstract). Gastroenterology 76: 1127, 1979. 5. FERRI?, J. P. Motricitk Gastro-Intestinale chez le Rat. Nature et Variations Physio-Pathologiques (Thesis 3rd Cycle). Toulouse, France: Ecole Nat. Vet., 1981, p. 124. 6. GREGORY, P. C., V. RAYNER, AND G. WENHAM. The influence of intestinal infusion of fats on small intestinal motility and digesta transit in pigs. J. Physiol. Lond. 379: 27-37, 1986. 7. LATOUR, A. Un dispositif sample d’analyse quantitative de l’electromyogramme intestinal chronique. Ann. Rech. V&t. 4: 347353,1973. 8. LATOUR, A., AND J. P. FERRY. Computer-aided analysis of gastrointestinal myoelectrical activity. J. Biomed. Eng. 7: 127-132, 1985. 9. RUCKEBUSCH, Y., AND J. C. BRADY. Recording and analysis of electrical and mechanical activity of the gastrointestinal tract. In: Techniques in Digestive Physiology, edited by C. Titchen. County Clare, Ireland: Elsevier, 1972, p. l-28. 10. RUCKEBUSCH, Y., AND L. B&NO. Electrical activity of the ovine jejunum and changes due to disturbances. Dig. Dis. Sci. 20: 10271034,1975. 11. RUCKEBUSCH, M., AND J. FIORAMONTI. Electrical spiking activity and propulsion in small intestine in fed and fasted rats. Gastroenterology 68: 1500-1508, 1975. 12. RUCKEBUSCH, Y., M. PAIRET, AND J. I,. BECHT. Origin and characterization of migrating myoelectric complex in rabbits. Dig. Dis. Sci. 30: 742-748, 1985. 13. SIM, M. K., AND J. M. E. LIM. Adrenergic receptor-mediated response of the rabbit small and large intestine. Jpn J. Physiol. 33: 409-413,1983. 14. SJOVALL, H., M. JODAL, AND 0. LUNDGREN. Further evidence for a glucose-activated secretory mechanism in the jejunum of the cat. Acta Physiol. Stand. 120: 437-443, 1984. 15. WISEMAN, G. Absorption of amino acids. In: Handbook of Physiology. Alimentary Canal. Washington, DC: Am. Physiol. Sot., 1968, sect. 6, vol. III, chapt. 67, p. 1277-1309.

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