The Motor Mechanism of Plants

atCSi^euheart at itS aPPearance has the same tubular ornb ,1} ' tlle simple tube very lapidly becomes modified, partly bv twistinc ?n itself partly by the outgrowth of the dorsal or the ventral wall of the tube to form the cavities of he auricle and ventricle.'— Starling, Principles 0 1 Human Physiology , 1920, p. 991. F peristalsis of the stomach or of the intestine is not rapid, it is easier to follow it and thus to discover the fundamental laws of peristalsis, as well as the special conditions which determine the unidirectioned propulsion of the solid or semi-fluid contents of the organ.

The difficulty encountered in obtaining an accurate record of the automatic pulsation of the stomach is very great. A method often employed is to insert into the gut an air- hlled balloon connected with a recording tambour. the introduction of the balloon causes distension and introduces many complications, as noted in the following quotation from Starling : ‘ Since (pulsations) may apparently arise at any portion of the gut which is subject to any special tension, it is not easy to be certain that a contraction recorded at any point is really propagated from a point two to three inches higher up.’ 1

It was therefore necessary to devise a special apparatus for the record (1) of the automatic pulsation of the alimen¬ tary canal, and (2) of the peristaltic wave initiated in the organ originally at standstill. The Pmstaltograph (fig. 170) consists of a fixed V-shaped rod and a movable vertical lever ; the preparation of the stomach is placed between the two and is kept in position by means of two pins. 1 he passage of the peristaltic wave moves the primary lever either inwards or outwards. Ibis slight movement is further magnified by a wheel of small diameter which is made to rotate in one direction or the other by the peristaltic expan¬ sion or contraction of the stomach. A long writing-lever attached to the rotating wheel marks successive dots at intervals of 1 or 2 seconds by the electro-magnetic device previously described ( cf . fig. 7). The compound magnifica¬ tion produced by the primary and the recording-lever is

either 100 or 200 times. The first is quite sufficient for general purposes ; the second is employed for record of relatively feeble pulsation. The magnification can, however, be readily increased to 500 times, when it is easy to record pulsations which had hitherto remained undetected. The experiments were carried out with the stomach of the frog and the intestine of the tortoise, ’mostly in the Stomach fixed by two pins ; a, upper or cardiac end ; b, lower or pyloric end. Specimen to be placed in vessel v, tilled with Ringer-Tyrode solution, oxygen being made to bubble through. Ihe vertical primary lever attached to small wheel ; r, recording-lever ; g, smoked-glass plate.

months of December and January, when many of the frogs were already hibernating and were therefore practi¬ cally inactive. The nondiibernating specimens with thick stomach-wall were found to be active, exhibiting vigorous pulsations. Several experiments were carried out in early spring (February), the activity of the specimens being then exceptionally great. There was also this difference between the wintei and spring- specimens . the prepared winter- specimens maintained their vitality for more than 24 hours, whereas the spring-specimens, under the prevailing higher

temperature, lost their power of response in less than 12 hours. The heart exhibits a descending scale of automatic activity from the sinus, where it is highest, to the tip of the ventricle where automaticity is practically absent. Similarly, the automaticity of the alimentary canal is most pronounced in the stomach, whereas it is apparently absent in the intestine, the pulsatory activity of which is induced only under the action of external stimulation. In the stomach itself the excitability is very much greater at the upper or cardiac end than at the lower or pyloric end.

The pulsations of the stomach are, generally speaking, '] extremely irregular. They exhibit all types of variation similar to those of the heart or those of the Desmodium leaflet . There are thus periodic groupings, also charac- i t eristic notches at systole or diastole. I was, however, 1 successful in obtaining more or less uniform pulsation ■ (1) by removing the contents of the stomach, which caused distension and continuous irritation of the organ, and (2) by ‘ reducing the shock-effect of the operation of dissecting out the stomach. This was accomplished by temporarily benumbing the tissue by application of ice.

Experiment 180. — A common type of record is a feeble pulsation followed by a large one, and this in recurrent series (fig. 177) ; after th;s, the pulsatory activity tends to become approximately uniform, as seen in fig. 178, in which the quicker up-curve was completed in 8 seconds, whereas the down-curve of recovery occupied the longer period of ( 30 seconds. There was a subsequent pause which lasted for 25 seconds. In summer-specimens the pulsations are very much quicker. Variation of the rhythmic rate effected by external agents chiefly affects the intervening pause, wlncn becomes shortened or prolonged unde, induced enhancement j or depression of rhythmic activity. Variation of tempera-

ture was found to induce a very marked change in the frequency of pulsation. FrG. 177. Record of automatic pulsations of Frog’s stomach, alternately of large and small amplitude. I now demonstrate the identical character of the rhythmic mechanism of the peristaltic action of the cardiac and alimentary tissues by the following series of tests. The oxygen contained in the tissue suffices for the con¬ tinuation of pulsation for a time in the absence of a fresh supply ; but prolonged deprivation of oxygen causes arrest of pulsation in both animal- and plant-tissues. I he asphyxia¬ tion produced by C02 causes arrest of the heart-beat and

Fig. 179. Arrested pulsation of stomacL due to lack of oxygen, revived by application of 02 (Frog). of the pulsation of Desmodium, the revival being pro- duced by application of oxygen (cf. Experiments 161, 162, 163. 164). Similar results were obtained with the animal Experiment i8j.. — 1 he preparation of frog s -stomach wasjj kept immersed in normal Ringer-1 yrode solution; the < bubbling of oxygen was discontinued and the pulsation became arrested after several hours. 1 nat this was uut toJ the lack of oxygen became at once evident by the revival ufl pulsation on addition of oxygenated water to the solution

Experiment 182. — On allowing C02 to bubble through the solution in which the frog’s stomach was immersed, the pulsation became arrested. Gradual r application of C02 Fig. 180. Effect of C02 on normal pulsation of Frog’s stomach. produc2d a preliminary enhancement followed by depression rnd arrest under continued application. The arrested pul¬ sation under C02 can, however, be revived by immediate substitution of oxygen for carbonic acid gas (fig. 180).

The rhythmic activity of both the Desmodium leaflet and the animal heart becomes slowed dovvn and arrested at a tiiermometric minimum. Rise of temperature, on the other hand, enhances the frequency of pulsation. The results are .0 .^oiiie extent medihed by the temperature to which the organisms had been accustomed ( cj . Experiment 171). Experiment 183. — Very similar effects are observed in the pulsation of the Aomach of the frog. Thus, in a par- ticular specimen the arrest at thermometric minimum

occurred at 10 0 C., the pulsation being revived by a rise . of temperature above this critical point. The frequency j underwent continuous increase with rise of temperature ; the amplitude of pulsation at 3 70 became so reduced that the Fig. 181. Effect of variation of temperature on pulsation of Pulsation came to a stop at thermometric minimum of ic° C. Rise of temperature enhanced the frequency. At 370 there was an apparent arrest; pulsation, however, revived on return to normal room-temperature n'.

pulsatory activity appeared to have been abolished. I hat .•* this was not the case became clear on allowing the tempera¬ ture to fall to that of the room, when the pulsations became r almost as vigorous as at the beginning (fig. 1S1). Both the leaflets of Desmudium and the frog’s heart are brought to a state of standstill by +he condition of sub- tonicitv. A feeble stimulation then causes a single response, while a stronger stimulation gives rise to a series of multiple responses. The persistence of the revived pulsation depends, moreover, on the amount of stimulation (cf. Experiments 146,

Precisely1 similar effects are observed in the response of the stomach. 1'he tonic condition of the isolated stomach was found to undergo decline till the pulsation came to a state of standstill. Hie following experiments describe the effect of external stimulation in reviving the rhythmic activity. Experiment 184. Effect of feeble stimulation. — The quiescent stomach was stimulated directly ; a single feeble 1 K,. ib2. Uniform responses of quiescent stomach under successive feeble electric stimulations (Frog).

electric shock was found to give rise to a single response ; the uniformity of the successive responses thus induced is shown in fig. 182. Fig. 183. Four recurrent responses under moderate stimulation. Fig. 184. Stimulus of intensity 2 applied aor 2 seconds gave rise to 8 recurrent pulsations (the movement of the recording plate was slowed down to half) (Frog). Experiment 185. Ejfect of moderate stimulation.— Electric stimulation of moderate intensity (1 unit) was applied for 1 second ; a series of 4 recurrent responses was now obtained in the place of a single response under feeble stimulation. Note the gradual decrease of amplitude and the prolongation of period of the successive pulsations

Experiment 186. Effect of prolonged and stronger stimula¬ tion. — The duration of application of stimulus was prolonged to 2 seconds and the intensity increased to 2 units. The result, was 8 recurrent pulsations recorded on a slower moving smoked plate (fig. 184). The persistence of pulsatory activity thus depends on the amount of stimulation. Experiment 187. — Chemical stimulation also revives the activity of the tissue previously in a state of standstill. I give a record (fig. 185) which shows the revival of activity

Fig. 185. Stimulating ; ction of Spt. Amraon. Aromat.in reviving in a quiescent stomach by the application of Spiritus Ammon iae Aromaticus. Fresh bile from an animal was also found to be a very effective stimulant in reviving or enhancing the activity of the stomach. Contractions causing movement onwards are generally known as peristalsis, and those in the opposite direction, antiperistalsis.1 The wave propagated in the normal direc¬ tion from the tipper (cardiac) end of the stomach A to the lower (pyloric) end B is designated as the peristaltic. Under certain circumstances the wave may become antiperistaltic, the direction of propagation being reversed from B to A. What are the laws which determine the direction of propaga¬ tion ? Experiments carried out with the stomach of the frog throw much light on the subject.

Normal peristalsis. — It is of much interest in this con¬ nexion to consider the phenomenon of peristalsis in the heart. The activity of its constituent parts is found to be very different, that of the sinus being very great, while that of the ventricle is exceptionally *feeble. The sequence of normal pulsation is sinus, auricle and ventricle, the direc¬ tion of propagation being determined by the differential activity at the two ends of the organ. In other -words, the propagated impulse follows the activity-gradient (rum the more active to the less active region.

Reversed peristalsis (antiperistalsis). — The natural dif¬ ferential activity may, however, be reversed by artificial means; for example, by loc^l stimulation of the relafively inactive ventricle. Thus it is possible to raise the activity Df the ventricle to a higher pitch than that of the sinus, with the result that the direction of propagation is now reversed, the sequence being ventricle, auricle and sinus. Even in this case the propagated impulse follows the activity- gradient from the activated to the less active end.

The differential activity at the two ends of the organ which determines the direction of peristalsis thus depends (1) on natural differential activity at the twro ends of the organ, and (2) on differential activity artificially nduced by activation of one end of the organ by local stimulation. ® The normal peristaltic and the reversed antiperistaltic waves can be clearly demonstrated in the quiescent stomach by the application of stimulus alternately at the upper cardiac end A and at the lower pyloric end B. The re- :ording point of the Peristaltograph is half-way between the two ends.

When stimulus is applied at the upper end A, the excita¬ tory peiistaltic wave generated by it, travels in the normal Erection and reaches the recording point Stimulation if B gives rise, on the other hand, to a reversed anti- leristaltic wave which also reaches the recording point. The ntensities of the transmuted peristaltic and antiperistaltic waves are shown by the amplitude of the responses in the •wo cases. Experiment 188. Mechanical stimulation. — A pinch wras applied first at the upper end A ; the transmitted effect of :his in the normal direction gave rise to a single response if large amplitude. The antiperistaltic wrave caused by pinching B also gave ris j to a single response, the amplitude

of which was about four times smaller. The transmitted effect in the normal and usual direction is thus considerably greater than that in the reversed direction (fig. 186). I obtained similar results with thermal stimulation. Fig. i 86. Responses to mechanical stimulation applied at upper end a, and lower end b (Frog) Experiment 189. Effect of electric stimulation. — This mode of stimulation has the special advantage of securing uniformity of stimulation at the two ends. The time of

Fig. 187. Responses to electric stimulation successively applied at a, at b, and once more at a (Frog). transmission in the two directions can aiso be determined with greater accuracy. The course of experimental procedure was as follows . the recording point was exactly half-way between A and B, so that the distance of transmission was the same in the normal and in the reversed direction. The record of the transmitted peristaltic excitation due to stimulation of A was first taken, then the record of the antiperistaltic trans¬ mission of the effect of stimulation of B. Finally, to make allowance for any possible change of excitability, a third record was taken of the effect of stimulation of A. The result shows that the excitability had undergone no change during the period of the experiment.

The intensity of the peristaltic transmission was found to be about four times greater than that of the antiperistaltic transmission (fig. 187). The time of transmission of the former was only 2-5 seconds, whereas that of the latter was 11 seconds or about four times longer. Experiment 190. Effect of distension. — -Internal disten¬ sion has been shown to induce revival of pulsation in both the Desmodium leaflet and the heart. Distension of the stomach was produced alternately at the A and B ends by the forcible introduction of a plug of cotton-wool, which acted as a constant mechanical stimulus. The effect is shown in fig. 188. The feeble pulsation at the beginning became greatly enhanced by the mechanical distension at A. Withdrawal of the plug was followed by enfeeblement of pulsation. 1 he plug was next introduced at the end B, with the result of enhanced pulsatory activity which was less intense than that induced by the stimulation of the upper end A.

I next describe tl e effects of continuous application of chemical and thermal stimulation. In order to avoid useless Fig. i 88. Effects of successive distension of a and b ends. a, feeble existing pulsation ; persistent enhancement of pulsation by mechanical distension of a end by introduction of a plug ; a', return of feeble pulsation aftei withdrawal of plug. Intro¬ duction of plug at b end gives rise to persistent pulsation less intense than that caused by distension of a end.

Fig. 189. Effect of continuous chemical stimulation with Cholin repetition I will describe only the effect of application at the upper end A. Experiment 191. Effect of continuous chemical stimula¬ tion . — Bile extract is known to be a strong stimulant of the intestine. I applied solution of Cholin chlorate to the upper Fig. 1 go. Effect of unilateral thermal stimulation applied at ii in reviving the peristaltic activity of the stomach. end of a quiescent stomach ; this gave rise to vigorous and persistent pulsations (fig. 1S9).

Experiment 192. Effect of thermal stimulation . — The specimen had become subtonic and was in a state of stand¬ still. \ stream of warm water was now applied at the upper end A. this caused a revival of peristaltic activity (fig. 190). i he animal stomach exhibits rhythmic activity similar to that of the heart and to that of the pulsating 'leaflet of Desmodium . Ihe pulsating activity of the stomach is dependent on a supply of oxygen ; it becomes arrested by the asphyxiating action of C02.

d he frequency of pulsation is modified by variation of temperature ; it is slowed down and becomes arrested at a thermometric mLlmum. Icise of temperature, within limits, increases the frequency of pulsation. In the condition of subtonicity, the pulsation of the stomach comes to a standstill. In this state, a feeble stimulation causes a single response. Stronger stimulation, on the other hand, gives rise to a series of multiple responses. The persistence of the pulsatory activity induced depends on the amount of stimulation. A peristaltic wave may be initiated in a quiescent stomach by activating one or the other end of the organ by local stimulation. The excitation transmitted in the normal peristaltic direction is more in¬ tense than that transmitted in the reverse or antiperistaltic direction.

The different modes of stimulation employed to activate the organ are : (i) mechanical distension ; (2) electric stimula¬ tion ; (3) chemical stimulation; and (4) thermal stimulation. The results described show that the direction of propaga¬ tion is determined by the differential activity at the two ends of the organ. The Law of Propagation of the Peristaltic Wave may be expressed in two different ways : (1) The direction of propagation of the peri¬ staltic WAVE IS FROM THE MORE ACTIVE TO THE LESS