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Plastic organic scintillators have been tailored in composition to achieve ultra-fast temporal response, thereby enabling the design and development of fast neutron detection systems with high timing resolution. Eljen Technology's plastic organic scintillators -- EJ-230, EJ-232, and EJ-232Q -- are prospective candidates for use in emerging neutron imaging systems, where fast timing is paramount. To support the neutron response characterization of these materials, the relative proton light yields of EJ-230, EJ-232, and EJ-232Q were measured at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a broad-spectrum neutron source and a double time-of-flight technique, the proton light yield relations were obtained over a proton recoil energy range of approximately 300 keV to 4 MeV. The EJ-230, EJ-232, and EJ-232Q scintillators exhibited similar proton light yield relations to each other as well as to other plastic scintillators with the same polymer base material. A comparison of the relative proton light yield of different sized cylindrical EJ-232 and EJ-232Q scintillators also revealed consistent results. This work provides key input data for the realistic computational modeling of neutron detection technologies employing these materials, thereby supporting new capabilities in near-field radionuclide detection for national security applications., Comment: 10 pages, 8 figures

Organic scintillators doped with capture agents provide a detectable signal for neutrons over a broad energy range. This work characterizes the fast and slow neutron response of EJ-254, an organic plastic scintillator with 5% natural boron loading by weight. For fast neutrons, the primary mechanism for light generation in organic scintillators is n-p elastic scattering. To study the fast neutron response, the proton light yield of EJ-254 was measured at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a broad-spectrum neutron source and a double time-of-flight technique, the EJ-254 proton light yield was obtained over the energy range of approximately 270 keV to 4.5 MeV and determined to be in agreement with other plastic scintillators comprised of the same polymer base. To isolate the slow neutron response, an AmBe source with polyethylene moderator was made incident on the EJ-254 scintillator surrounded by an array of EJ-309 observation detectors. Events in the EJ-254 target coincident with the signature 477.6 keV $\gamma$ ray (resulting from deexcitation of the residual $^{7}$Li nucleus following boron neutron capture) were identified. Pulse shape discrimination was used to evaluate the temporal differences in the response of EJ-254 scintillation signals arising from $\gamma$-ray and fast/slow neutron interactions. Clear separation between $\gamma$-ray and fast neutrons signals was not achieved and the neutron capture feature was observed to overlap both the $\gamma$-ray and fast neutron bands. Taking into account the electron light nonproportionality, the neutron-capture light yield in EJ-254 was determined to be 89.4$\pm$1.1 keVee., Comment: 9 pages, 10 figures

Background: Organic scintillators are widely used for neutron detection in both basic nuclear physics and applications. While the proton light yield of organic scintillators has been extensively studied, measurements of the light yield from neutron interactions with carbon nuclei are scarce. Purpose: Demonstrate a new approach for the simultaneous measurement of the proton and carbon light yield of organic scintillators. Provide new carbon light yield data for the EJ-309 liquid and EJ-204 plastic organic scintillators. Method: A 33~MeV $^{2}$H$^{+}$ beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory was impinged upon a 3-mm-thick Be target to produce a high-flux, broad-spectrum neutron beam. The double time-of-flight technique was extended to simultaneously measure the proton and carbon light yield of the organic scintillators, wherein the light output associated with the recoil particle was determined using $np$ and $n$C elastic scattering kinematics. Results: The proton and carbon light yield relations of the EJ-309 liquid and EJ-204 plastic organic scintillators were measured over a recoil energy range of approximately 0.3 to 1~MeV and 2 to 5~MeV, respectively for EJ-309, and 0.2 to 0.5~MeV and 1 to 4~MeV, respectively for EJ-204. Conclusions: These data provide new insight into the ionization quenching effect in organic scintillators and key input for simulation of the response of organic scintillators for both basic science and a broad range of applications., Comment: 11 pages, 9 figures

An organic glass scintillator developed by Sandia National Laboratories was characterized in terms of its light output and pulse shape discrimination (PSD) properties and compared to commercial liquid (EJ-309) and plastic (EJ-276) organic scintillators. The electron light output was determined through relative comparison of the $^{137}$Cs Compton edge location. The proton light yield was measured using a double time-of-flight technique at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a tunable broad-spectrum neutron source and an array of pulse-shape-discriminating observation scintillators, a continuous measurement of the proton light yield was performed for EJ-309 (200 keV$-$3.2 MeV), EJ-276 (170 keV$-$4.9 MeV), and the organic glass (50 keV$-$20 MeV). Finally, the PSD properties of the organic glass, EJ-309, and EJ-276 were evaluated using an AmBe source and compared via a figure-of-merit metric. The organic glass exhibited a higher electron light output than both EJ-309 and EJ-276. Its proton light yield and PSD performance were comparable to EJ-309 and superior to that of EJ-276. With these performance characteristics, the organic glass scintillator is well poised to replace current state-of-the-art PSD-capable scintillators in a range of fast neutron detection applications., 32 pages, 13 figures, 9 tables

Compact neutron imagers using double-scatter kinematic reconstruction are being designed for localization and characterization of special nuclear material. These neutron imaging systems rely on scintillators with a rapid prompt temporal response as the detection medium. As n-p elastic scattering is the primary mechanism for light generation by fast neutron interactions in organic scintillators, proton light yield data are needed for accurate assessment of scintillator performance. The proton light yield of a series of commercial fast plastic organic scintillators---EJ-200, EJ-204, and EJ-208---was measured via a double time-of-flight technique at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a tunable deuteron breakup neutron source, target scintillators housed in a dual photomultiplier tube configuration, and an array of pulse-shape-discriminating observation scintillators, the fast plastic scintillator light yield was measured over a broad and continuous energy range down to proton recoil energies of approximately 50 keV. This work provides key input to event reconstruction algorithms required for utilization of these materials in emerging neutron imaging modalities., Comment: 15 pages, 6 figures

Herein we report the progress towards an organic glass scintillator with fast and thermal neutron sensitivity providing “triple” pulse shape discrimination (PSD) through the inclusion of a boron-incorporated aromatic molecule. The commercially available molecule 2-(p-tolyl)-1,3,2-dioxaborinane (TDB) can be readily synthesized in one step using inexpensive materials and incorporated into the organic glass scintillator at 20% by weight or 0.25% 10B by mass. In addition, we demonstrate that TDB can be easily scaled up and formulated into organic glass scintillator samples to produce a thermal neutron capture signal with a light yield equivalent to 120.4 ± 3.7 keVee, which is the highest value reported in the literature to date.

In these experiments a large portion of the pelvic ganglion of adult female rats was transplanted into the wall of the urinary bladder of the same animals. The morphology and fine structure of the transplants were studied in whole-mounts and in sections for light and electron microscopy, from two days up to four months after operation. The general architecture of the ganglion was preserved in all the transplants. The vascularization was re-established. Nerves grew out of the transplant and connections with the original intramural nerves of the bladder wall were established. All the synapses degenerated at the time of transplantation; new synapses began to reappear on the ganglion neurons in the oldest transplants. Although some neurons in the transplant degenerated during the first few days, the majority of neurons survived for the full length of the experiments (four months). Satellite glial cells and small intensely fluorescent cells had a similar structure and distribution as in control ganglia. The results show that the homotransplant of pelvic neurons into the bladder has a high rate of success, in terms of survival, maintenance of fine structure, growth and re-connections; these neurons of adult organisms display plastic and regenerative abilities.

The autonomic nervous system controls motility of the heart, gastrointestinal tract, urinary tract, and reproductive organs; the tone of blood vessels, lymphatic vessels, and airways; movement of the pupil and lens; and the activity of the muscles of hairs. It carries afferent impulses for these organs, leading to reflexes and to sensations, including visceral pain. Key components are assemblies of neurons in hypothalamus, brain stem, and spinal cord. Nerves connect these nuclei to ganglia outside the central nervous system. Subdivisions of the system are based on projections to different organs and on the distinct pathways of nerves and ganglia, sympathetic and parasympathetic ones, and enteric nerves.

The fine structure of taenia coli was studied by electron microscopy in guinea-pigs from birth to old age (over 2 years old). Smooth muscle cells are approximately 1,000 microm(3) in volume at birth, 2,200 microm(3) in young adults and 4,500 microm(3) in old age. Muscle growth and muscle cell enlargement continue throughout life, an increase in muscle volume of about 240 times. Differentiated muscle cells divide during development and in adults. Because mitoses are found in any part of the muscle, the tissue grows from within, rather than by addition at the ends or borders. There is progressive increase in nucleus volume, and decrease in surface-to-volume ratio and in nucleus-cell volume ratio in muscle cells. At all ages the taenia consists of a uniform population of muscle cells (apart from dividing cells); there are no undifferentiated cells, no precursor cells or myoblasts, and no degenerating cells. Interstitial cells and fibroblasts are observed at all ages with only small variations in relative number. The amount of intramuscular collagen increases in old age. There is roughly one capillary for every 170 muscle cell profiles at birth, and one for every 200 in adults and in old age. The innervation is dense and reaches all parts of the muscle. In adults there are approximately 1,300 axons per 10,000 microm(2) of sectional area, or between 8,000 and 38,000 axons in a full cross section of taenia; this amounts to approximately 2% of the muscle volume. An answer to the question of why there are so many nerves in the taenia was not found. Expanded axon profiles are part of typical varicose fibres. Varicosities are packed with small clear vesicles and lie at the surface of nerve bundles. Absence of strong, constant patterns indicating specialized contacts of the nerve terminals is a feature of these nerves at all ages. Some varicosities are closest to interstitial cells; more commonly they are close to muscle cells at sites that strongly suggest a neuro-muscular junction. The additional possibility that some varicosities are part of afferent fibres is discussed. The innervation is well developed at birth and the highest density of innervation is found around day 4 when 4% of the taenia consists of nervous tissue. The innervation of immature taenia is characterized by close juxtaposition of axons and muscle cells. Axon profiles packed with vesicles, varicosities and presumptive neuro-muscular junctions are present at birth. The extent of Schwann cells in intramuscular nerves is markedly less than in adults, and virtually all the axons have maximal membrane-to-membrane contact with other axons. In taenia of aged guinea-pigs, the density of innervation is reduced. There is no actual loss of nerve tissue; the total amount of nerve tissue is greater than in young adults, and the apparent reduction reflects a more intense growth of muscle cells. The Schwann cell component becomes more conspicuous than in young adults and there is a greater number of axons fully wrapped by a Schwann cell. Presumptive neuro-muscular junctions are common and probably commoner than in young adults. Growth of muscle cells, changes in their cytological features and in the stroma occur throughout life, including old age. Nerves too continue to grow and undergo structural changes in pattern of distribution, relation with Schwann cells and effector cells.

Adhesions in the peritoneal cavity have been implicated in the cause of intestinal obstruction and infertility, but their role in the aetiology of chronic pelvic pain is unclear. Nerves have been demonstrated in human pelvic adhesions, but the presence of pain-conducting fibres has not been established. The purpose of this study was to use an animal model to examine the growth of nerves during adhesion formation at various times following injury and to characterize the types of fibres present. Adhesions were generated in mice by injuring the surface of the caecum and adjacent abdominal wall, with apposition. At 1-8 weeks post-surgery, adhesions were processed and nerve fibres characterized histologically, immunohistochemically, and ultrastructurally. Peritoneal adhesions had consistently formed by 1 week after surgery and from 2 weeks onwards, all adhesions contained some nerve fibres which were synaptophysin, calcitonin gene-related peptide, and substance P-immunoreactive, and were seen to originate from the caecum. By 4 weeks post-surgery, nerve fibres were found to originate from both the caecum and the abdominal wall, and as demonstrated by acetylcholinesterase histochemistry, many traversed the entire adhesion. Ultrastructural analysis showed both myelinated and non-myelinated nerve fibres within the adhesion. This study provides the first direct evidence for the growth of sensory nerve fibres within abdominal visceral adhesions in a murine model and suggests that there may be nerve fibres involved in the conduction of pain stimuli.

The distribution of afferent axons in the bladder of rats was studied by means of immunohistochemistry for calcitonin gene-related peptide (CGRP), in frozen sections and in wholemount preparations of mucosa and muscle coat. Synaptophysin-immunofluorescence was used for the general detection of all intramural axons. The afferent axons were distributed over four distinct targets: at the base of the epithelium, inside the epithelium, on blood vessels (both arteries and veins) and along muscle bundles. In the mucosa, all the afferent axons, except the perivascular ones, lay either inside the epithelium or in a subepithelial plexus very close to the basal surface of the epithelium. The plexus was thickest in the neck of the bladder and in the initial portion of the urethra, and it became progressively less dense in the adjacent regions; it did not extend beyond the equatorial region, and therefore the mucosa of the cranial region of the bladder had no afferent axons. Most of the axons in the subepithelial plexus were terminal axons and included conspicuous varicosities arranged in very long chains; branching points were numerous, usually at right angles and located at the level of a varicosity; some axons split and then rejoined, forming closed axonal loops. The afferent innervation of the musculature was more diffuse, and appeared uniform throughout the bladder. After unilateral surgical denervation (by excision of the pelvic ganglion 5-7 days earlier) areas of complete denervation were observed, but there were large areas where the innervation was only reduced. The results showed that there is a bilateral innervation of many regions of the mucosa and the musculature, including individual muscle bundles. A substantial number of fibres crossed the midline into the contralateral side of the bladder. CGRP-immunofluorescence in mucosal afferent axons is enhanced in the surviving axons 5 days after contralateral denervation, a change which is interpreted as an early sign of regeneration.

Interstitial cells of Cajal (ICC) aroused much interest among neuroanatomists at the beginning of the century. These small cells, organized into networks, are intercalated between nerve fibers and muscle cells, and are now considered by many authors to be responsible for the pacemaker activity of the gut. Renewed interest in these cells arose recently when the receptor tyrosine kinase, c-kit, was shown to be associated with their functional activity. The embryonic origin of interstitial cells has remained a controversial issue ever since their discovery. Some authors consider them to be of neural or glial nature and thus of neural crest origin. Others consider them to be of fibroblastic or muscular nature. We have applied the quail-chick marker system to solve this problem. ICC were identified by means of a chicken-c-kit nucleic probe which cross-reacts with the quail c-kit gene product. We constructed chimeric bowels by grafting isotopically quail vagal neural crest into chick embryos at embryonic day 2 (E2). The enteric innervation of the chimeras was then of quail origin. In situ hybridization of the chimeric bowels showed that all the c-kit-positive cells were of the chick type, and therefore belonged to the gut mesenchyme and were not neural crest-derived cells. This observation was confirmed by culturing aneural chick guts on the chorio-allantoic membrane. Typical ICC, as defined at the EM level and by their expression of the c-kit receptor, developed in the gut wall in the complete absence of enteric innervation. One can conclude the ICC are of mesodermal origin and develop independently from enteric neurons with which they later establish anatomical and functional relations.

Smooth muscle is widespread; it is found in all viscera and vessels, and is a major component in the wall of all tubular organs (one of the few exceptions is the bile duct of some species, such as the rat, which has no muscle). The appearance of many smooth muscles under a microscope varies to an extent which is surprisingly small by comparison with the wide range of functional properties found in different muscles. Yet, the structure of the muscle, which comes to life only at the level of resolution that can be achieved by electron microscopy, has features which account for its different mechanical properties.

1. The lungs of five fetal (133-140 days gestation) and thirty-four postnatal (2-240 days) sheep were artificially perfused in situ with warmed and oxygenated sheep blood. In postnatal animals the airspace of the lung was filled with liquid similar in composition to fetal lung liquid. In fetal and postnatal animals luminal liquid volume was measured by the impermeant tracer technique. 2. Under resting conditions the pulmonary epithelium of fetal animals secreted liquid at a mean (+/- S.E.M.) rate of 2.0 (+/- 0.4) ml (kg body weight)-1 h-1, those of postnantal animals absorbed liquid at -1.8 (+/- 0.2) ml (kg body weight)-1 h-1. 3. Addition of 2,4-dinitrophenol to achieve a concentration of 1.5 x 10(-3) M in the perfusing blood in postnatal animals caused complete cessation of liquid absorption. 4. Light and electron microscopic examination of the lung after periods of up to 6 h of artificial perfusion showed no evidence of epithelial damage. From 3 h onwards, liquid accumulation was evident in the perivascular spaces. 5. Addition of adrenaline to the perfusate in fetal animals caused absorption of liquid to occur at a mean rate of -2.9 (+/- 1.3) ml (kg body weight)-1 h-1. In postnatal animals adrenaline caused the rate of liquid absorption to increase from a mean rate of -1.4 (+/- 0.2) to -2.2 (+/- 0.3) ml (kg body weight)-1 h-1. 6. In the fetus addition of amiloride (0.8 x 10(-4) M) to the luminal fluid blocked adrenaline-induced liquid absorption and caused secretion to occur at 1.3 (+/- 0.3) ml (kg body weight)-1 h-1. 7. In postnatal animals the response to amiloride was age dependent. In newborn lambs (2-14 days) amiloride blocked liquid absorption and caused secretion of liquid to occur in seven out of eight animals at a mean rate of 0.9 (+/- 0.3) ml (kg body weight)-1 h-1 (n = 8). In older animals (15-240 days) the characteristic response to amiloride was slowing of the rate of liquid absorption (mean rate of absorption,-0.2 (+/- 0.09) ml (kg body weight)-1 h-1, n = 18) with liquid secretion being seen in only three of eighteen animals.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Strips of taenia coli from the caecum of the guinea-pig were mounted in an organ bath at 37 degrees C; isometric contractions were elicited with 10(5)M carbachol. Each taenia was stretched to the length at which it produced the maximum active tension; it was then fixed and embedded for measurement of the transverse sectional area. 2. The maximal force produced ranged between 96-1 and 138-3 mN. This corresponded to a force of between 251 and 513 mN.mm(2) (mean: 416 +/-28 [n = 10]). Temperature changes in the range 23-38 degrees C had little effect on the maximal force output.3. When allowance is made for the extracellular space (about 32% of the transverse sectional area), for the non-muscular cells present in the taenia (about 5%), and for the non-contractile material present in the muscle cells (about 10%), the maximal force generated was about 734 mN.mm(2) of contractile material (or almost twice as large as in skeletal muscle).4. Electron microscopy revealed terminal apparatuses at the ends of muscle cells, anchoring the cells to the connective tissue, and cell-to-cell junctions (attachment plaques). In addition, many dense patches of dense bands, sites near the cell surface where filaments are seen to end, were scattered along the entire length of the muscle cell and lay close to bundles of collagen fibrils. 5. It is suggested that the production of such a large force by this smooth muscle is partly explained by the lateral attachment of some contractile units to sites along the entire cell length, which in their turn are anchored to the collagen network; the latter may be considered a sort of intramuscular tendon.

—The concentration of noradrenaline was studied in the proximal colon of the guinea-pig, where intrinsic adrenergic neurons are present in the myenteric plexus. The noradrenaline content is higher than in the myenteric plexus of other parts of the alimentary tract. After extrinsic denervation of the colon, about 25% of the original content of noradrenaline remains in the myenteric plexus, and this is considered to be the amount due to the intrinsic adrenergic neurons; also a substantial noradrenaline uptake activity is still detectable. On the other hand, in the part of the wall formed by circular muscle-submucous plexus-submucosa-mucosa, which has control values close to those of the ileum, extrinsic denervation causes a nearly complete depletion of noradrenaline. This is considered as evidence that the intrinsic neurons do not project to the circular musculature, or the submucosa or mucosa.

By a specific histochemical method for the detection of catecholamines, a large number of adrenergic fibres was observed in the rabbit foliate and circumvallate papillae. Adrenergic fibres run in the corion, in close relationship with the basal pole of taste buds. These observations support the hypothesis of a sympathetic control over gustatory input.

The concentrations of noradrenaline, dopamine and 5-hydroxytryptamine were studied in the stomach, duodenum, ileum, caecum (taenia coli), colon and rectum of the guinea pig. The wall of the alimentary canal was dissected into two fractions, one formed by the longitudinal muscle and myenteric plexus, the other formed by circular muscle, submucous plexus, submucosa and mucosa. In the longitudinal muscle-myenteric plexus, the amount of noradrenaline was lower in the ileum (0.56 μg/g of fresh tissue), higher in the duodenum and caecum (0.75 μg/g and 0.82 μg/g respectively) and even higher in the stomach and rectum (0.85 μg/g and 0.91 μg/g). The highest value was found in the colon (1.33 μg/g), probably related to the occurrence of intramural adrenergic neurons. When extrinsic nerves to the ileum were damaged, the amount of noradrenaline in the corresponding ileal segment was reduced to less than 5 per cent within 3 days in both fractions of the wall. 6-Hydroxydopamine (35 mg/kg intravenously) reduced to approx. one-third the amount of noradrenaline in longitudinal muscle-myenteric plexus of ileum and colon. Reserpine (1 mg/kg, subcutaneously injected 72 h-earlier) reduced the amount of noradrenaline in the longitudinal muscle-myenteric plexus of both ileum and colon to 0.01 μg/g. Doses of reserpine as small as 0.02 mg/kg were still effective in causing a great reduction in noradrenaline concentration. No difference in the effects on ileum and colon was observed.

This brief article reviews some aspects of the ultrastructure of the enteric ganglia which have been brought to light by electron microscopy. The ganglion neurons are surrounded by a vast neuropil in which axons, dendrites and glial cells with their processes are tightly packed together. Blood vessels and connective tissue do not penetrate into the ganglia but lie outside them. The exclusion of connective tissue from the ganglia takes place during embryonic development and is complete soon after birth. By ultrastructural criteria it has proven difficult to classify neuronal cell types, in spite of the differences in their functional specializations and their projections. The glial cells are rich in gliofilaments and have processes which are firmly anchored to the surface of the ganglion. Glial cells outnumber ganglion neurons and probably confer structural stability to the ganglia and at the same time allow substantial changes in the shape of the ganglia and in the arrangements of its elements to occur when the adjacent muscle layers contract. Numerous specialized contacts are found between vesicle-containing nerve endings and glial cell bodies or glial processes. The question of how freely substances diffuse inside a ganglion, along the narrow spaces between processes and cell bodies, remains to be answered. Since parts of the surface of many neurons are directly covered by the basal lamina of the ganglion and by connective tissue, certain substances of the interstitial space may have direct access to the nerve cells. Investigations on the intraganglionic nerve endings have provided several classifications of axonal types, mainly based on the appearance of their vesicles. However, these classifications are tentative and are in many respects still uncertain. The great majority of endings originate from intrinsic neurons and synaptic specializations are commonly encountered.

The circular musculature of the guinea-pig ileum has been studied by freeze-fracture to analyze quantitatively the gap junctions (nexuses) between its smooth muscle cells. The average cell surface area and cell volume are 5,074 micron 2 and 3,260 micron 3. The packing density of nexuses is 48/1,000 micron 2 of cell surface or approximately 244/muscle cell. Nexuses range in area from less than 0.1 to approximately 1.5 micron 2 and they occupy 0.212% of the cell surface. The average packing density of intramembrane particles or pits in nexuses is approximately 7,200/micron 2 of nexal surface, indicating that there may be approximately 77,000 intercellular channels in the full complement of nexuses of one muscle cell.

A histochemical technique was used to stain the myenteric neurons in the intact wall of the small intestine of mice, guinea-pigs and sheep. The length and diameter of the small intestine and the total serosal surface area were also obtained. Myenteric neurons were counted on large whole-mount preparations of the muscularis externa. Counts were carried out also on the submucosal plexus, on a more limited scale. In the mouse a spatial density of 10,600 myenteric neurons per cm2 was found. The small intestine was 33 cm long and measured on average 11.5 mm in circumference, the total outer surface (serosal surface) amounting to about 38.0 cm2. The total number of myenteric neurons in the small intestine was calculated as about 403,000. In the guinea-pig the length of the small intestine was 145 cm, the average circumference 22 mm and the total outer surface area about 319 cm2. The neuronal packing density was 8600/cm2, and the total number of myenteric neurons about 2,750,000. In the sheep the small intestine was about 2100 cm long with an average circumference of 60 mm and a total surface area of about 12,600 cm2. The ganglion neuron density was about 2500/cm2, and the total number of myenteric neurons in the small intestine was calculated as about 31,500,000. Thus, in the sheep the small intestine contained about 11 times as many myenteric neurons as the guinea-pig and about 80 times as many as the mouse. The differences are in the same direction as, but not proportional to, the differences in body weight and in the length of the intestine. The neuronal spatial density was highest in the mouse and lowest in the sheep, and in the sheep the neurons were markedly larger, and gathered in ganglia that were larger and further apart from one another, than in the mouse, while they had intermediate values in the guinea-pig. A new way of expressing neuronal packing densities is presented together with the proposal of an arbitrary but reproducible unit of intestinal length (a segment whose length is equal to its diameter). In the submucosal plexus the neuronal density was about 3000/cm2 in the guinea-pig, about 8700/cm2 in the mouse and about 4500/cm2 in the sheep. In the mouse the submucosal neuron density decreased gradually along the length of the small intestine.

A conspicuous smooth muscle (of transverse sectional area comparable to that of the taenia coli) situated in the suspensorium ovarii and in the ligamentum ovarii proprium of the guinea-pig is described. The muscle is attached to the last rib, it reaches the medial side of the ovary, to which it is loosely attached; it passes beyond the caudal pole of the ovary (from which it receives additional muscle bundles), it approaches the oviduct, passing ventral to it, then it spreads around it and eventually reaches the distal end of the uterus; this muscle (which is here indicated as costo-uterine muscle) is in direct continuation with, or transforms itself into, the longitudinal outer coat of the uterus.

The ultrastructure of the glial cells in the enteric plexuses of the rat, guinea-pig, rabbit, cat and sheep has been investigated by freeze-fracture and by thin-section electron microscopy. In all the ganglia studied, glial cells outnumber neurons. They are readily identified by their shape, position and ultrastructure (particularly the abundant amount of gliofilaments) but could not be subdivided into separate types. They provide a partial sheath to the ganglion neurons (but large areas of neuronal membrane lie directly beneath the basal lamina and collagen fibrils) and have long laminar processes extending between nerve processes. Most nerve processes are in direct membrane-to-membrane contact with each other; the glial cells only separate groups of them and rarely form a sheath around an individual neurite. The gliofilaments are anchored to conspicuous dense bodies beneath the cell membrane at the surface of ganglia. The possible significance of these systems of gliofilaments (and the high number of intermediate junctions) is discussed in the light of the severe mechanical stresses imposed on the ganglia by the contractile activity of the gut wall. Numerous specialized contacts, of unknown significance, are found between vesicle-containing nerve varicosities and glial cell bodies or glial processes. In freeze-fracture preparations (cat and guinea-pig), a specific pattern of intramembrane particles allows the cell membrane of the enteric glial cells to be readily identified.