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Recent reports have suggested that carcinoma of the tonsil and adjacent structures (tonsillar pillars, adjacent soft palate and lateral pharyngeal wall) can be treated with improved survival rates by combining definitive surgery with planned preoperative radiotherapy. Experience to date does not clearly demonstrate the ideal dose of preoperative radiotherapy; however, in general it appears that survival rates improve in proportion to increasing dosage of preoperative radiation. The use of preoperative radiation in doses approaching or exceeding tumoricidal levels (6,000-6,500 rads at approximately 1,000 rads/week) has been limited by the unacceptable complication rate to be expected. The rate of major complications reported has ranged from 18 percent to almost 47 percent. For the past three years, all patients seen by the Department of Otolaryngology of the Upstate Medical Center with malignancies involving the tonsil and its adjacent structures have been managed by a combined modality of 5,500 rads preoperative radiotherapy followed by definitive surgical resection, using distant, unirradiated flaps for repair where necessary. There were 33 patients in the group, including three T2, 20 T3 and 10 T4 lesions. Joint evaluation and planning of treatment between radio-therapy and otolaryngology coupled with meticulous attention to various aspects of surgical management has yielded the results reported in the table. The major complication rate has been limited to 3.03 percent. These results indicate that it is possible to undertake extensive resections for carcinoma of the tonsil and adjacent structures after high-dose preoperative radiotherapy without incurring any significant increase in morbidity over surgery alone.

Eighty-nine unselected women to undergo caesarean section were induced intravenously with either 20 mg diazepam (45 patients) or 200 mg thiopentone (44 patients). To facilitate intubation suxamethonium was injected 1 min after the induction agent and was also given by continuous infusion throughout the procedure. The patients were ventilated with N2O/O2 (3:2). Immediately after delivery all the mothers received 50 mg pethidine and 100 mg thiopentone intravenously. Unpleasant recollections and dreams occurred in 23% of the thiopentone series and in only 2% of the diazepam series. No significant difference in the condition of the neonates in the two series could be detected. One woman received 120 mg diazepam intravenously for the control of epilepsy shortly before delivery without apparent ill effect on the neonate. The incidence of moderate to severe suxamethonium pains was 33% in the diazepam series and only 14% in the thiopentone series. In elective caesarean sections with normal preinduction values of serum creatine phosphokinase, the postoperative rise in the serum activity of this enzyme was significantly higher in the diazepam mothers compared to those who had received thiopentone. Thiopentone therefore in some way protects against suxamethonium-induced muscle pains as well as liberation of creatine phosphokinase from the muscles. It is suggested that this is due to the deep level of anaesthesia occurring 1 min after 200 mg thiopentone in contrast to the semiconscious state occurring after 20 mg diazepam. ZUSAMMENFASSUNG 89 nicht ausgewahlte Frauen, bei denen eine Sectio caesarea vorgesehen war, wurden i.v. entweder mit 20 mg Diazepam (45 Patientinnen) oder mit 200 mg Thiopental (44 Patientinnen) eingelehet. Suxamethonium wurde eine Minute nach der Anaesthesieeinleitung zur Erleichterung der Intubation und anschlieRend als Dauertropfinfusion wahrend der Operation gegeben. Die Patientinnen wurden mit N2O/O2 (3:2) beatmet. Unmittelbar nach der Geburt erhielten alle Mutter 50 mg Pethidin und 100 mg Thiopental i.v. Unangenehme Erinnerungen und Traume traten bei 23% der Thiopentalserie und nur bei 2% der Diazepam-Patientinnen auf. Bezuglich des Zustandes der Neugeborenen konnte kein Unterschied zwischen den beiden Gruppen festgestellt werden. Eine Frau bekam kun vor der Geburt 120 mg Diazepam i.v. als Epilepsieprophylaxe, ohne daR sich ein offensichtlicher nachteiliger Effekt fur das Kind ergab. In der Diazepamserie sahen wir bei 33%, in der Thiopentalserie jedoch nur bei 14% der Patientinnen mittelstarke bis schwere. Suxamethoniumschmerzen. Bei den elektiven Kaiserschnittpatientinnen mit normalen Vonverten der Serum-CPK ergab sich unter den Diazepam-Muttern ein signifikant hoherer postoperativer Anstieg der Serumaktivitiit dieses Enzyms verglichen mit denen, die Thiopental erhalten hatten. Thiopental scheint also bis zu einem gewissen Grad Schutz gegen Suxamethonium-bedingte Muskelschmerzen ebenso wie gegen die CPK-Freisetzung aus der Muskulatur zu bieten. Wir glauben, das dies der tieferen Narkose eine Minute nach 200 mg Thiopental zuzuschreiben ist, gegenuber dem Zustand einer HalbbewuRtlosigkeit nach 20 mg Diazepam.

Changes in plasma potassium following modified electroconvulsive therapy ‘were investigated using four induction agent-relaxant combinations. Small rises were found for three of the four regimes, but only methohexitone-suxamethonium was associated with a rise significantly greater than that in the control group. There was no correlation between the changes in plasma potassium and the degree of modification of the seizure. In no patient was a dangerous level of hyperkalemia found to occur.

In 23 healthy young pigs stress was produced by preventing escape behavior by pharmacologic restraint (Celocurin chloride). In comparison to nine control animals, severe acute cardiopathy was observed in all experimental pigs. In 13 per cent of the animals sudden death occurred. By histologic examination fragmentation, granulation, and necrosis of cardiac cells, with interstitial reaction developing within 24 to 48 hours, was found in all stress-subjected animals. Major ECG changes were T wave inversion, arrhythmias, and transitory lifting of the ST segment. Results are discussed from a comparative point of view. A much higher sensitivity of the myocardium of the pig in comparison to that of the rat or the dog usually used in strees experiments is presumed.

Using a radiologic technique, the position and pattern of movement of the diaphragm have been evaluated in three adult volunteers, both awake and anesthetized, during spontaneous ventilation and with muscle paralysis and mechanical ventilation. Studies were made with the subjects in supine and left

A clinical trial was conducted in hospital using apparatus designed for anaesthesia for domiciliary midwifery. Patients presenting for minor gynaecological surgery were anaesthetized and subsequently interviewed to ascertain their reaction. Anaesthesia was induced with methohexitone and muscle relaxation was obtained with suxamethonium. Maintenance of anaesthesia was achieved with a 50% mixture of nitrous oxide and oxygen supplemented with trichloroethylene 0.25%. The apparatus and anaesthetic technique proved satisfactory in clinical practice with some minor complications.

The effect of different types of acidosis on sensitivity to neuromuscular blocking agents was studied in vivo on the tibialis muscle of cats and in vitro in the phrenic nerve diaphragm preparation of the rat. In vivo metabolic acidification was caused by diffusion of weak organic acids, which penetrate easily into the cell and imitate closely the state of metabolic acidosis in man. Respiratory acidosis was caused by inhalation of 10% carbon dioxide in oxygen. In the in vitro experiments, acidification was caused by titration with the same acids as well as hydrochloric acid. pH was lowered to levels just above 7.0. Blank in vivo studies showed that the metabolic acidosis by itself causes no significant depression of indirect muscle contraction, while respiratory acidosis causes only a slight depression. A minor depression was seen in the blank in vitro metabolic acidosis studies. Both succinylcholine and decamethonium blocks are strongly antagonised in vivo and in vitro by metabolic and respiratory acidosis. Pancuronium bromide block was potentiated by metabolic and respiratory acidosis both in the in vivo and in vitro experiments. It is most likely that changes in transmembrane potential are the cause for the changes in sensitivity seen in these experiments. ZUSAMMENFASSUNG Der Einfluss verschiedener Arten von Azidose auf die Empfindlichkeit fur muskelerschlaffende Mittel wurde mit Hilfe von in vivo Experimenten auf den Tibialis-Muskel der Katze und in vitro Experimenten auf das Phrenicus-diaphragma-Praparat der Ratte untersucht. Die metabole Azidose wurde in vivo durch schwache organische Saure hervorgerufen, welche schnell in die Zelle hineintreten und der metabolen Azidose beim Mensch am nachsten stehen. Respiratorische Azidose wurde durch Inhalation von 10% Kohlensaure im Sauerstoff hervorgerufen. In den in vitro Experimenten wurde die Azidose durch Titration der Spulflussigkeit mit den selben Sauren und mit Salzsaure hervorgerufen. Das pH wurde bis gerade oberhalb 7.0 herabgedruckt. Blanke in vivo Experimente zeigten, dass die metabole Azidose selbst keine signifikante Erniedrigung der indirekten Muskelkontraktion ergibt und respiratorische Azidose nur eine leichte. Auch in den in vitro Experimenten wurde eine leichte Depression durch die metabole Azidose festgestellt. Die Muskelerlahmung durch Succinylcholine und Decamethonium wurde durch metabole und respiratorische Azidose in vitro und in vivo starkstens antagonisiert. Muskelerschlaffung durch Pancuronium wurde aber durch metabole und respiratorische Azidose in gleiche Weise in den in vitro und in vivo Experimenten potenziert. Die Anderungen des Ruhepotentials der Zellmembrane werden als verantwortlich fur die Empfindlichkeitsveranderungen angesehen.

The effects of succinylcholine (SCh) on both normal and immobilized canine gastroenemius muscle were compared and contrasted with respect to potassium (K+) flux, VO2, and muscle tension. Muscle K+ efflux and VO2, increased more in immobilized atrophie than in normal muscle. Neither normal nor immobilized muscle showed increased tension with SCh. K+ efflux from immobilized atrophic muscle was much less than that previously demonstrated from denervated muscle. The difference in response, however, cannot be attributed solely to the absence of supersensitivity in muscle with immobilization atrophy, for paraplegic muscle, which also does not manifest supersensitivity, responds to SCh with a large release of K+. It may be that there is a trophic function from upper to lower motor neuron, as well as from lower motor neuron to muscle.

Thirty patients received general anaesthesia for forty intralaryngeal operations using a laser beam. The essential requirements for the anaesthetic management are: (1) Anaesthetic agents should be non-flammable. (2) Small diameter red rubber cuffed tracheal tubes provide maximum working space for the surgeon, facilitate controlled ventilation and minimize the explosion hazard of anaesthetic gases in the vicinity of the laser beam. (3) Continuous muscle relaxation of head and neck and of laryngeal muscles facilitates the instrumentation and lasing of lesions of vocal cords which are thus rendered fixed and immobile.

Summary. Two groups of patients were submitted to electric convulsive therapy, one without pre-treatment (ECT) and the other after administration of thiopentone and succinylcholine (modified ECT). After ECT, there was a large increase in the blood level of catecholamines (noradrenaline+adrenaline), of factor VIII and of plasminogen activator. After modified ECT, the release of catecholamines and of factor VIII was significantly reduced, but hyperfibrinolysis took place as in ECT. These results suggest that while catecholamines are probably not responsible for plasminogen activator release during stress, adrenergic mediation of the concomitant increase in factor VIII is highly probable.

Precurarization with a protective dose of d-tubocurarine, 6 mg in the adult male, 4 mg in the female, was achieved in a series of 100 patients three minutes before the induction of anaesthesia. This procedure was well tolerated on both psychological and physiological bases. The patients displayed no modification of their respiratory mechanics and could exhibit normal coordinated movements of their hands, legs and head. Slight diplopia and a sensation of drowsiness occurred frequently.

The effects of the prostaglandins E2 and F2α on bronchotonus were studied in cats anesthetized with chloralose, vagotomized, relaxed by suxamethonium, and ventilated at a constant tidal volume. Under conditions of normal bronchotonus, PGE2 (0.5–10 μg/kg) had a weak and PGF2α (0.1–50 μg/kg) a moderate bronchoconstrictor effect; in the case of PGE2 only, there was a clear correlation to the concomitant rises in pulmonary arterial pressure. During bronchoconstriction induced by infusion of 5-HT, carbachol or paraoxon, PGE2 had a dose dependent bronchodilator effect in the majority of the experiments. Some cats, however, reacted with a further increase in airway pressure to this prostaglandin. PGE2 had no dilator effect when bronchoconstriction had been induced by histamine. Experiments in which the cats were treated with α-methyltyrosine, guanethidine, cocaine, reserpine, phentolamine, propranolol, chlorisondamine or atropine did not reveal a dependence of the bronchial actions of the prostaglandins on the autonomic nervous system or its transmitters. Inhibition of prostaglandin synthetase by indomethacin increased sensitivity to both the constrictor and dilator effects of both prostaglandins.

The effects on dynamic and static components of the afferent stretch response from a muscle were examined in the period after a brief tetanus, which previous study has shown is marked by a persisting elevation in sensory discharge. Afferent activity of the cat's triceps surae or medial gastrocnemius muscle was monitored as integrated multiunit discharge in a whole dorsal root, and the ventral roots were stimulated to produced a tetanus. The levels of activity at a static muscle length were found to be elevated in decreasing degree over several millimeters of lengthening beyond that at which the muscle was held during tetanus. During a ramp stretch, the velocity-related overshoot in dorsal root activity was also increased. Such changes were still detected after the elevated discharge had been made to disappear by momentary limited extension of the muscle. They are consistent with the hypothesis of residual effect on the intrafusal fibers, perhaps in the form of persisting actin-myosin crossbridges. Under sinusoidal stretch, the multiunit responses were generally decreased in the first few cycles following tetanus. Observations on single units indicated that the decrease was due chiefly to diminished responses of Ib afferents, which had incompletely recovered from adaptation brought on by excitation during the tetanus.

Due to its ease of administration and the widespread familiarity with electroconvulsive therapy (ECT), most psychiatrists become facile in its use without the usual background information customarily thought appropriate for most treatment modalities. It is almost paradoxical that this widely administered treatment is used frequently with limited awareness of what effects, other than clinical effectiveness, could and do occur. Consequently it is important to review the vast amount of research that has been done in the area. This seems an essential underpinning for a common treatment modality that still requires future theoretical insights regarding its efficicacy. The history of the convulsive therapies is well known. 1–5 During this development there has been documentation of the use of ECT in almost every diagnostic category of the standard nomenclature. The conditions for which ECT has been used are summarized in Table 1. However, most contemporary authors and practitioners feel that it is most indicated for treatment of severe depressions and secondary for very retarded or excited conditions. It is widely used for these disorders, perhaps in part due to the relative lack of contraindications to treatment. Particular contraindications to ECT seem to depend largely on the predilections of the author consulted. While Kalinowski states that there are no absolute contraindications to ECT, save brain tumor, 6 others, such as Perrin, cite a long list. 7 Obviously one is obliged to weigh therapeutic needs against the limited but very real liabilities of the treatment modality. Table 2 summarizes the contraindications to ECT that have been cited. The complications of ECT have been numerous, particularly with the use of unmodified treatment. These have been mitigated, or in some instances added to, by the use of various anesthetic and muscular-relaxant agents. Table 3 summarizes the complications that have been reported. Most of these complications are relatively benign, and there is a low mortality risk associated with the use of ECT. Table 4 summarizes the mortality data in large samples, as well as specific case reports. Although much of the foregoing is usually embodied in clinical experience with the modality, the convulsive stimulus and the convulsive and other physiologic responses are less well known. It is the intent of this paper to review these aspects of ECT in some detail.

An understanding of the maintenance of normal body temperature, and the manner in which surgery, anaesthesia, and related procedures may disturb thermoregulation, is of considerable importance in paediatric anaesthesia. The subject of accidental hypothermia, with particular reference to the newborn infant, is reviewed; and hyperpyrexia is briefly discussed.

Dose-response curves of succinylcholine (SuCh) were obtained in anesthetized patients by means of mechanograms of the flexion-grip response of the hand to ulnar nerve stimulation. A subparalyzing dose (0.04 mg/kg b.w.) of d-tubocurarine (d-TC) administered prior to SuCh (0.025–1.6 mg/kg b.w.) exhibited a shift of the dose-response curves toward the right, i.e., a diminishing effect on magnitude and duration of the SuCh induced neuromuscular blockade. The effective dose of SuCh required to produce a half-maximal inhibition of the contractile force (ED50, 0.12 mg/kg before d-TC) was increased to 0.3 mg/kg (15 min after d-TC), 0.26 mg/kg (after 30 min), and 0.23 mg/kg (after 45 min). Thus, d-TC pretreatment employed under clinical conditions to prevent potential hazards of SuCh requires a significant larger dose of SuCh to ensure consistently adequate relaxation. ZUSAMMENFASSUNG Dosis-Wirkungsbeziehungen von Succinylcholin (SuCh) (0,025–1,6 mg/kg Korpergewicht) wurden mit Hilfe von Mechanogrammen der Beuge- und Faust-schlusbewegung der Hand nach elektrischer Ulnarisreizung an narkotisierten Patienten ermittelt. Die Vorausinjektion von d-Tubocurarin (d-TC) in der unterschwelligen Dosierung von 0,04 mg/kg Korpergewicht fuhrte zu einer Rechtsverschiebung der Dosis-Wirkungskurven von SuCh, d.h. d-TG vermindert Ausmas und Dauer der neuromuskularen Hemmwirkung von SuCh. Die Effektivdosis von SuCh, die eine halbmaximale Hemmung der Kontraktionskraft bewirkt (ED50; 0,12 mg/kg ohne d-TC) steigt auf 0,3 mg/kg 15 min nach d-TC an bzw. 0,26 mg/kg (nach 30 min) und 0,23 mg/kg (nach 45 min). Wird unter klinischen Bedingungen vor einer SuCh Injektion ein Muskelrelaxans vom kompetitiven Typ, z.B. d-TC verabfolgt, um potentielle Nebenwirkungen von SuCh zu verhuten, ist eine hohere Dosis SuCh erforderlich, um immer eine gute Muskelerschlaffung zu gewahrleisten.

The extraction of suxamethonium from urine samples in the form of its ion-pair complex with bromothymol blue is described. Detection of the drug was accomplished colorimetrically and enzymically using two thin-layer chromatography systems, and one gas chromatographic method. A brief study was made of the stability of suxamethonium at various pH values which affect its storage in urine for different periods of time. The extraction technique and colorimetric method of detection were applied to other quaternary ammonium compounds, some of which had been recovered from blood and urine after addition to these fluids. This work also included a short study of the effect of certain tertiary amine drugs if present in the urine with the quaternary compounds.

Current developments in the pharmacology of neuromuscular blocking agents indicate that within the next several years, nondepolarizing drugs of short and intermediate duration of action, devoid of significant side effects, may become a reality. The important factors which may permit their development are reviewed.

Pancurofnium bromide and its deacetylated metabolites were determined in human urine after intravenous administration to five patients by two methods : ion-pair extraction with bromophenol blue for the quaternary nitrogen and hydroxamic acid method for the acetyl group. Succinylcholine which was administered simultaneously was confirmed not to be extracted as the ion-pair complex at all. For the assay of the acetyl group, pancuronium and its metabolites were isolated from the urine as the ion-pair complex followed by column chromatography. The extracts were also subjected to silica gelthin-layer chromatography, wherein pancuronium and its three deacetylated metabolites could be separated while the dye went away to the top of the plate. The results revealed that approximately 20 to 50% of the dose was recovered in the urine during 24 hr period after administration, mostly in the first 3 to 4 hr period, and that pancuronium was excreted mainly as the unchanged form with a slight amount of its mono- and dihydroxy metabolites. The extractability of quaternary ammonium ions with a wide variety of structure as ion-pair complex with bromophenol blue was examined in order to find any relation to the structure. It was revealed that the extractability is determined mainly by two factors, that is, the lipophylic character of the ammonium ion and the steric effect around the cationic head and the value of the sum of π-constants for four groups plus that of Es parameters for three smallest groups can provide an approximate measure for predicting the extractability.

Expiratory muscle activity has been studied in the external oblique muscle during anaesthesia with spontaneous breathing in twenty-two patients. Expiratory muscle activity was absent in all subjects before induction but developed within 29 minutes of induction in twenty patients, remaining absent in the other two. Deepening the level of halothane anaesthesia reduced, but in only one case abolished, expiratory muscle activity. Endo-tracheal intubation and passage of a pharyngeal airway had no effect other than initial stimulation and relief of obstruction when present. Topical analgesia of larynx had no effect. Surgical stimulation and respiratory obstruction both caused marked increase in expiratory muscle activity.

SUMMARY In anaesthetized open-chest dogs, neuromuscular blocking doses of tubocurarine reduced phasic aortic flow, aortic blood pressure, stroke volume, heart rate, cardiac output and peripheral resistance. These haemodynamic effects could be attributed to blockade of sympathetic ganglia and to histamine release. Paralyzing doses of gallamine slightly increased phasic aortic flow, stroke volume and cardiac output; such changes could be related to cardiovagal block. Blood pressure and peripheral resistance were slightly reduced. Contrary to known effects in anaesthetized patients, gallamine or atropine did not produce important tachycardia in anaesthetized dogs. Suxamethonium caused a small reduction in peripheral resistance; phasic aortic flow, stroke volume and cardiac output were slightly increased. These minor circulatory disturbances may be attributable to muscarinic effects of the drug.

The effects of edrophonium and choline have been compared with those of the depolarizing substances acetylcholine, decamethonium, and suxamethonium, in both innervated and chronically denervated tibialis anterior muscles of cats under chloralose anaesthesia. Both edrophonium and choline were more potent antagonists to paralysis by tubocurarine than could be accounted for by their ability to stimulate the motor end-plates directly. It appeared likely that direct depolarization of the end-plate played no part in the anti-curare action of edrophonium and only some part in the anti-curare action of choline. A paralysis produced by the neuromuscular blocking agent, benzoquinonium, was more readily antagonized by a tetanus or by acetylcholine, suxamethonium, and decamethonium than a similar paralysis produced by tubocurarine. The tetraethyl ammonium ion was also slightly more effective against a paralysis by benzoquinonium. On the other hand, edrophonium was about 300 times and choline about five times less potent as an antagonist to benzoquinonium than to tubocurarine. Furthermore, the previous administration of benzoquinonium abolished the antagonistic action to tubocurarine of normally effective doses of edrophonium and reduced that of choline. These results were similar to those previously obtained with neostigmine, physostigmine and ethyl pyrophosphate and suggested that there was some similarity in the mechanism of action of all of these substances. Benzoquinonium, therefore, showed promise as a useful pharmacological tool for distinguishing compounds with this particular type of action. These anti-curare compounds did not appear to act by cholinesterase inhibition, not by an increase in the sensitivity of the motor end-plates. In common with other workers, we suggest that there is a pre-synaptic mechanism of action.

Twenty-two mongrel dogs were employed for an investigation of the circulatory actions of succinylcholine in the presence of nitrous oxide, halothane anaesthesia.

SUMMARY 1 The effects of procaine and lidocaine on neuromuscular transmission were determined in man. 2 These agents when injected intravenously did not decrease the twitch response. However, if a partial neuromuscular block was produced by succinyl-choline or d-tubocurarine, the block was increased by procaine or lidocaine. 3 A neuromuscular blocking action of procaine and lidocaine could be demonstrated following intra-arterial injection. 4 A decrease in respiration or apnea could be produced by doses of procaine and lidocaine which did not depress neuromuscular transmission. 5 It was suggested that although local anesthetic agents may affect the motor nerve terminal, the release of ACh, and skeletal muscle directly, at present the neuromuscular blocking activity of local anesthetics appears to be attributable mainly to their acetylcholine inhibiting action at the motor end plate.

L'auteur passe en revue les etudes que l'on a faites sur l'emploi des stimulus en-gendrant la repugnance, ou de la diethylamide de l'acide lysergique dans le traitement de l'alcoolisme. Ces stimulu...

SUMMARY A survey of the reported responses of myotonic patients to depolarizing relaxants reveals the variable incidence and extent of induced myotonia. Generalized myotonia due to suxamethonium is described in a patient with myotonia congenita and, from subsequent investigations during a second operation, the action of the drug is clarified. Such a myotonic response is attributed to fasciculation, and a normal depolarizing block was demonstrated with continued administration of the drug. Suggestions are made for the anaesthetic management of such patients.

An anaesthetic technique for adenotonsillectomy, successfully used in 650 children, is described. Premedication includes morphine in addition to trimeprazine and atropine. Following thiopentone and suxamethonium-aided intubation, anaesthesia is maintained by controlled hyperventilation with nitrous oxide and oxygen via a modified Rees circuit, employing a combined T-piece and modified Worcester connection, to simplify the use of the Doughty tongue-blade, and firm thermoplastic endotracheal tubes to resist blade compression. Continuity of relaxation is provided by intermittent injections of suxamethonium. The authors' orotracheal assembly is unobtrusive, secure and ensures a patent airway with minimal deadspace. Airway resistance changes are readily appreciated. The technique makes for perfect airway control, relaxation for surgical access, and rapid recovery.

1. 1. The direct response of suprasylvian gyrus of succinyl-cholinized unanesthetized cats was studied with minimal stimulation and responses averaging. Excitability cycles were determined by paired stimulation, the intervals between conditioning and testing stimuli being 0.25–500 msec. 2. 2. There is an initial period of augmented responsiveness, lasting about 5 msec, followed by a period of depression, maximal at about 10 msec, and with a variable rapid phase of recovery followed by a prolonged mild depression (occasionally augmentation) up to 500 msec. 3. 3. The absence of detectable latency and absence of early refractory period suggest that the dendrites are directly excited. 4. 4. A positive potential parallels the period of early depression. Both occur sooner with increased strength of stimulus, and the onset of depression occurs later after intravenous nembutal. It is suggested that both the depression and the positive potential represent activation of inhibitory mechanisms.