NERVOUS SYSTEM
The nervous system is divided into a peripheral portion and a central portion.
The peripheral nervous system (PNS) is on our menu for today and the central
nervous system (CNS) for tomorrow.
 | CNS |
Peripheral
Nervous system
Objectives
You should be able to:
1. identify the following in the class slide sets:
| Sensory ganglion | ||
| ganglion
cell satellite cells | |||
| Autonomic ganglion | |||
| sympathetic ganglion | |||
| multipolar neuron | |||
| postganglionic sympathetic neuron | |||
| myenteric ganglion | |||
2. distinguish myelinated and unmyelinated axons in peripheral nerves with the following stains:
Masson stain
Bodian stain
H&E
3. recognize small branches of nerves running in connective tissue.
* * * * *
|
Blue Histology |
Slides
| D-24 | Carotid sheath (elastic stain) | |
| D-26 | Subclavian artery (H&E) | |
| D-92 | Tongue (Masson stain) | |
| D-107 | Lower duodenum (H&E) | |
| D-182 | Peripheral nerve (Masson stain) | |
| D-183 | Peripheral nerve (Bodian stain) | |
| D-184 | Sympathetic ganglion (H&E) | |
| | D-188 | Spinal cord with spinal ganglia.(H&E) |
| Your slide set has alternative slides for most of the structures to be seen in this lab: | ||
|
D-25 | A peripheral nerve (the ulnar nerve) with Masson stain | |
| D- 96 | An H&E section of tongue with very small nerve bundles | |
|
D-114 | A slide of the colon showing enteric ganglia | |
|
D-185 | A spinal ganglion stained with silver to show cell processes well. | |
| D-189 | The trigeminal (sensory) ganglion | |
Slide descriptions
D-182 Peripheral nerve (Masson stain)
Hold this slide up and note that it includes both a transverse (cross-section) and a longitudinal section of a conventionally preserved peripheral nerve. Examine the transverse (cross) section first because it is easier to understand. Then, move on to the longitudinal section and find the same structures in it.
The transverse section appears as a circular piece of tissue with about 15 bundles of axons (illustration). Each of these is a fascicle of nerve fibers separated by connective tissue. The slide illustrates the connective tissue components well since it is stained with Masson stain. The epineurium, or outermost protective layer, consists of dense connective tissue, rich in collagen fibers. Next is the perineurium surrounding each individual fascicle. It is composed of several layers of Schwann cells (or close relatives of them). These form a grey colored, epithelial layer that isolates the bundle of axons from the surrounding connective tissue. It encloses a fluid filled space that you see as a small gap between the perineurium and the underlying nerve axons. The connective tissue within the perineural sheath is endoneurium. It includes seams of loose connective tissue to provide pathways for small arterioles and venules, as well as delicate reticular fibers around individual axons (illustration). Fibroblasts secrete the Type I collagen fibers and their nuclei can be seen in the green seams of endoneurium. Schwann cells secrete the reticular fibers around themselves.
Turn your attention to the axons. It is important to choose an area where they have been sectioned exactly in cross section. The large ones are wrapped in layers of myelin. These myelin sheaths are composed of layer upon layer of Schwann cell membrane. (A dental model for myelin would be to take the cap off a tube of toothpaste and wind the tube from the back end around the handle of a toothbrush, squeezing the toothpaste out in the process. In the case of a myelinated nerve the axon is wrapped with dozens of layers of double cell membranes of Schwann cells with no cytoplasm between them.) The Blue Histology program has an animation of how myelin forms.
However, histological processing extracts the lipids and shrivels the axons. The space formerly occupied by the myelin is generally empty with just wisps of protein left. Where the preservation is very good the entire area occupied by the myelin has an orange spider web of orange protein throughout with an orange dot, the axon itself, in the middle. Frequently the protein shrinks to give the appearance of an orange donut with the axon in the center. In other cases the protein collapses around the edge of the space or around the axon giving a clear round hole. Even the axon may glomp onto the edge of this space instead of running down the middle. Look for these patterns (illustration).
The nuclei of the Schwann cells can be distinguished from those of endoneural fibroblasts or endothelial nuclei by shape and location. Think about this and then find examples of both. Since the tiny blood vessels tend to run longitudinally you should be able to pick out the endothelial cells with little problem other than a bit of thinking. Of course, none of the nuclei belong to neurons.
Small axons are not wrapped in a myelin sheath. Instead, they are grouped in clusters and surrounded by the cytoplasm of Schwann cells. Look carefully at the figure in your textbook to understand this relationship. Then identify on your slide, clusters of unmyelinated axons around a Schwann cell (whose cytoplasm stains green in this preparation).
Now turn to the longitudinal section. It contains the same structures as seen in the transverse section and gives you a chance to figure out what these elongate structures look like from a different perspective.
The oblong nuclei within the bundles of axons belong to Schwann cells. Pick out the myelinated axons as lumpy orange lines surrounded by cobwebby layers of myelin protein. Once you see them, it is easy to pick out the nodes of Ranvier. Use your text to understand exactly what these nodes are and what their physiological significance is. You will not be able to pick out small unmyelinated axons in this longitudinal section because the section is thicker than the axons, so other tissue above and below masks them. You can, however, find seams of endoneural loose connective tissue (with some fibroblast nuclei) and perineural sheaths of flattened Schwann cells (illustration).
D-183 Peripheral nerve (Bodian stain)
Again, your slide includes a longitudinal and a transverse section of a peripheral nerve, this time stained with silver. Although the axons are somewhat shriveled, this sort of staining nicely complements the more conventional ones. It specifically stains the axons and nuclei. Cytoplasm and cell membranes (myelin) are unstained. However, if you look very carefully you can see ghosts of the outer boundary of some myelin sheaths in cross section.
Silver stains are particularly useful for demonstrating small unmyelinated fibers, which often run in clusters. Begin by distinguishing axons from Schwann cell nuclei in the transverse section (illustration). Next, distinguish myelinated from nonmyelinated axons (illustration). Myelinated axons are separated from each other by substantial space. The unmyelinated fibers are narrower and in clusters. Now, imagine how these axons should show up in the longitudinal section and please yourself by finding that they do, indeed, look just like you imagined (illustration).
D-26 Subclavian artery (H&E)
The cross section here is much the same, as that in D-182 except that it has been stained with H&E. Try to find each of the structures that you found in the cross section with the Masson stain; epineurium, perineural sheath, endoneurium with capillaries and fibroblasts, myelinated axons (and nonmyelinated ones?), Schwann cell nuclei. Most sectioned nerves that you will be seeing from now on probably will be stained with H&E so it is useful to examine this slide even if it is a bit harder to interpret than a trichrome stain section.
D-24 carotid sheath (elastic stain)
The vagus nerve, shown here, consists almost entirely of small, unmyelinated fibers. The axons themselves look like hollow tubes. Search around for areas where they have been cut as transversely as possible. Be able to tell that almost all of the axons are unmyelinated by finding the occasional myelinated axon for comparison. This distinction is not too hard to make, once you understand what to look for (illustration). An aid is that the elastic stain colors the remnants of myelin protein black. The slide shows plenty of Schwann cell nuclei, and nicely demonstrates blood vessels and connective tissue layers.
As you noted in an earlier lab session there is little elastica in the epineurium. Nerves are extremely tough to break but not elastic at all.
D-188 Spinal Cord and spinal ganglia.(H&E)
The spinal ganglia ( = dorsal root ganglia) are important components of the peripheral nervous system, but disregard the spinal cord until the next laboratory session on the central nervous system. Hold the slide up and note that the main mass of tissue is the spinal cord (with its telltale butterfly-shaped gray matter at the center). The two extensions are spinal nerves projecting out as far as the dorsal root ganglia. Of course the nerves extend much farther but they run out of the plane of section after the ganglia in this slide. Examine the ganglia. They contain the cell bodies of the sensory neurons. Because their axons are very long sensory neurons have large cell bodies. These have a finely granular distribution of Nissl material, a large pale nucleus and prominent nucleolus. The abundant small, darkly staining cells are satellite cells. They form a sheath one cell deep around each ganglion cell body.
The ganglion also has to have nerve fibers (axons) running through it, going to and from the ganglion cells. However, the axons strongly tend to clump together and the cell bodies do likewise, illustration (like oil and water in a salad dressing or, to reuse an analogy, genders at an Australian dinner party).
Appreciate that sensory neuron cell bodies are the metabolic centers, maintaining the long processes of the sensory neurons. There are no synapses onto them. Therefore, the cell bodies can be closely packed together with little space between them, aside from the satellite cells. These neurons are unipolar (or "pseudobipolar") with only one process extending from the cell body. After a short distance the process bifurcates with one branch running out to the periphery and the other into the spinal cord. The simple shape of these neurons allows the satellite cells to form a fairly regular single layer around each cell body (illustration).
D-184 Sympathetic ganglion (H&E)
D-184 shows an excellent example of a sympathetic chain ganglion. Follow the short segment of nerve cut in longitudinal section until you find a large swelling, containing numerous cells. The most prominent are the large neurons with large round nuclei, distinct nucleoli, and granular Nissl bodies in the cytoplasm. There are vast numbers of satellite cells, and most of the axons in this ganglion are unmyelinated (illustration).
* * * * *
This is an appropriate time for you to review the organization of the autonomic system in your textbook. Appreciate that an autonomic ganglion has a fundamentally different function from a sensory ganglion. A single sensory neuron runs all of the way from a sensory organ, say in the skin, to the spinal cord. In contrast, two neurons make up an autonomic pathway (both sympathetic and parasympathetic). The first preganglionic neuron has its cell body in the spinal cord or brain and sends its axon out to make a synaptic contact with the dendrites or cell body of the second postganglionic neuron. That second neuron sends its axon to the distant target, maybe a glandular cell or smooth muscle cell. The ganglion is where the postganglionic neuron cell bodies are clustered together and also where their dendrites and synapses are. The ganglion cells are multipolar with multiple dendrites for synapses to form on. Therefore, the satellite cells surrounding them cannot form tidy sheets but look scattered (illustration). Also, there is a substantial amount of neuropil in the ganglion, that is, blank-looking areas where invisibly tiny branches of axons and dendrites intertwine and synapse. The way to distinguish sympathetic from sensory ganglia is to remember the differences in their functions and hence structures.
Presumably the autonomic nervous system uses a two-neuron strategy as an amplification mechanism. A single preganglionic neuron in the spinal cord may synapse with two dozen postganglionic neurons.
D-107 Lower duodenum (H&E)
A plexus of specialized autonomic ganglia called enteric ganglia innervates the smooth muscle of the gut wall. These are more complex than sympathetic or parasympathetic ganglia because they also contain sensory neurons, interneurons and astroglia-like cells. They are able to generate peristaltic waves independently from stimuli from the CNS and, indeed, the gut actually has more neurons in it than the spinal cord! (This is why "gut courses", like histology, are so easy.) The enteric ganglia form two plexuses of ganglia. Examine the easily seen myenteric plexus today and wait until the laboratory session on the digestive system to look for the smaller, more elusive submucosal plexus.
Start by recognizing the epithelial, connective tissue and muscle layers of the duodenal wall. The myenteric ganglia are scattered along the junction between the longitudinal and circular muscle layers of the muscularis externa. They appear as balls of cells, each with a few large neurons, (illustration). These neurons have typical ganglion cell bodies with large pale nuclei and prominent nucleoli. They are surrounded by small satellite cells, which account for most of the cell nuclei of the ganglia (Illustration). The ganglia communicate with one another by a network of nonmyelinated axons which are difficult to observe with H&E staining. The plexus can be likened to a fishnet with the knots being the ganglia and the strings being the bands of axons running between the knots.
D-92 Tongue (Masson)
The nerves that you have looked at so far are large ones. As they extend out into the body, nerves branch into smaller and smaller divisions. Even the tiny branches retain their basic structure; in particular, their perineural sheath of flattened Schwann cells. Look around in the connective tissue between the muscle fibers for nerve bundles of various sizes (illustration). Some will have only several axons. Can you tell whether the axons are myelinated or not? If you snoop hard enough you may find a parasympathetic ganglion. It will be regulating the activity of some of the extensive glands in the tongue. (How did I know that this was not a sympathetic ganglion?)
* * * * *
The peripheral nervous system includes many structures which can be tricky to visualize, as you know by now. Therefore, if you wish you can look at a parallel set of slides to confirm that you understand the structures that you have just looked at.
|
| A peripheral nerve (the ulnar nerve) with Masson stain | ||
|
| An H&E section of tongue with very small nerve bundles | ||
|
| A slide of the colon showing enteric ganglia | ||
|
| A spinal ganglion stained with silver to show cell processes well. | ||
|
| The trigeminal (sensory) ganglion |
* * * * *
Objectives
1. To be able to identify the following structures:
| Neuron | Spinal cord | Cerebrum | ||||
| cell body | dorsal horn | pyramidal cells | ||||
| Nissl substance | ventral horn | astrocytes | ||||
| dendrite | lateral horn | |||||
| nucleus | motor neuron | Meninges | ||||
| nucleolus | interneuron | dura | ||||
| central canal and | subdural space | |||||
| Nervous tissue | ependymal lining | arachnoid | ||||
| white matter | nerve rootlets | subarachnoid space | ||||
| gray matter | pia | |||||
| neuropil | Cerebellum | |||||
| astrocytes | cortex | Ventricles | ||||
| oligodendrocyte | molecular layer | choroid plexus | ||||
| ependymal cells | Purkinje cells | ependymal cells | ||||
| endothelial cells | granule cell layer | |||||
| granule cells | ||||||
| * * * * * | ||||||
|
Blue Histology |
Slides
| D-181 | Optic nerve, cross-section (H&E) | |
| D-188 | Spinal cord (H&E) | |
| D-192 | Spinal cord (silver stain) | |
| D-194 | Spinal cord (Kluever stain) | |
| D-195 | Cerebral cortex (stained for astrocytes) | |
| D-196 | Cerebellar cortex (H&E) | |
| D-197 | Cerebellum (Bodian stain) | |
| D-198 | Cerebrum (Kluever stain) | |
| D-199 | Choroid plexus (H&E) |
Slide descriptions
D-194 Spinal cord (Kluever stain)
Slide D-194 contains sections through the spinal cord, cut at four different levels. The Kluever stain renders myelin blue; cell nuclei, purple; Nissl substance (clumps of rough ER) pink; and general cytoplasm colorless. Hold the slide up to the light. The blue outer portion of the cord is white matter. It is composed of tracts of axons running up and down the spinal cord (and hence cut transversely). The gray matter is the pale, butterfly-shaped inner area. Distinguish the dorsal horns, which are thinner and extend out to the edge of the tissue section, from the ventral horns, which appear as rounder bulges surrounded by white matter. In the center lies the central canal.
The ventral horn is distinctive by having the largest neurons in the spinal cord. These motor neurons show up particularly well in the lumbar section. Their axons project via ventral roots to innervate the skeletal muscles. These giant cells have very conspicuous Nissl granules and multiple dendrites. Observe them at 400X. There are many other small cell nuclei in the gray matter. Some are small interneurons. Most are glial cells.
The dorsal horn has many small interneurons but none comparable in size to the giant motor neurons of the ventral horn. Be sure that you understand why. At the edge of the gray matter between the dorsal and ventral horns is the lateral horn. This is where the preganglionic cell bodies of the autonomic system are located (where do their axons go?) You can see the lateral horn as a distinct bulge in at least one of your sections and as a zone with several large neurons in others (illustration). The thoracic section probably shows this best.
Most of the small, "bare" nuclei scattered throughout both the white and gray matter belong to glial cells. Start by examining them in white matter, so you can be sure that you are not confusing glia with small neurons. It should not be difficult to convince yourself that two main categories of cells are present (illustration, higher mag.). The larger, paler nuclei, with somewhat irregular shape belong to astrocytes. The smaller, denser, conspicuously round nuclei, which look like lymphocyte nuclei, are oligodendrocytes. These latter form the myelin in the central nervous system. In addition, a small number of dense, elongated nuclei belong to microglia. Be careful, though, some of them are endothelial cells of the numerous capillaries. Capillaries cut in cross section are easy to recognize but if only an endothelial cell nucleus shows it can be hard to identify.
Astrocytes and oligodendrocytes can also be distinguished from one another in gray matter (higher mag.). Here, they can be distinguished from medium sized neurons, which show off a bit of Nissl substance, but not from the tiniest neurons. If you look in the white matter then all of the nuclei belong to glia cells.
The fourth type of glial cell in the CNS is the ependymal cell. It lines the central canal of the spinal cord and the ventricles of the brain. Ependymal cells usually form a cuboidal to columnar epithelium in the cord and a low cuboidal lining in the ventricles.
D-181 Optic nerve, cross-section (H&E)
Special protective sheets of connective tissue, called meninges surround the entire central nervous system. These were poorly represented on the preceding slide because they had been dissected away. They are nicely preserved around the optic nerve on slide D-181. The optic nerve actually is misnamed. It is not a true nerve at all. The retina is a genuine part of the CNS and so is the tract of axons which connects it with the brain. As part of the CNS, the optic nerve is surrounded by the three meninges (illustration).
The outermost thick, dense, fibrous layer is the dura mater (literally "hard mother"). Almost invariably the dura separates from the underlying arachnoid in fixed material. Understand that this subdural space is an artifact and that the subdural space normally is only a potential space. The thinner arachnoid layer is the physiological barrier between the CNS and the rest of the body. It corresponds to the perineural sheath of a peripheral nerve in structure, embryonic origin and function. Underlying the arachnoid is the subarachnoid space filled with cerebral spinal fluid. Short trabeculae traverse this space to anchor the arachnoid to the pia below. The pia mater ("faithful mother") is an ordinary connective layer that is attached to the outer surface of all CNS tissue. In the optic nerve, and only here, pia invades from the surface to divide the axons into fascicles (illustration).
The axons of the optic nerve happen to be nonmyelinated on your slide but have a myelin sheath for most of their length. Glial cell nuclei are very obvious among them (illustration).
D-188 spinal cord with spinal ganglia H&E
It is worth seeing how neurons and glial cells appear with conventional H&E staining that you are used to. Motor neurons are well preserved. Again, about all that you can see of the glial cells are their nuclei and a tiny rim of cytoplasm that stains paler than the surrounding tissue (illustration).
All three meningeal layers cover the spinal cord, and extend over the dorsal root ganglia (illustration). However, almost all of the dura has been cut away from spinal cord, and most of the arachnoid layer has also been lost as well. Where the arachnoid can be seen, it is recognizable as a very attenuated epithelial layer. Pia is obvious here, being composed of ordinary connective tissue with collagen and fibroblasts.
Note the nerve rootlets running in the subarachnoid space (illustration). Nerve fibers emerge from the dorsal horn and enter the ventral horn all along the spinal cord. All of the fibers under one vertebra collect together to form a pair of spinal nerves. To do so, some fibers must run for a short distance up or down along the cord after they emerge. As they do they collect into bundles called rootlets, which finally come together as two roots (a dorsal root and a ventral root). The two roots come together at the level of the spinal ganglion to form a spinal nerve. Here you can see these rootlets (sectioned transversely) running along the surface of the cord.
This slide has the best preserved white matter (as well as gray matter) found in your set (illustration). Nonetheless, myelin sheathes have been extracted, and the axons are considerably shriveled in the spinal cord. It is very hard to avoid this sort of artifact which affects the large axons more than the little ones. The myelin of the nerve rootlets is more easily preserved than that within the white matter of the spinal cord. Spend some time looking at these superbly preserved axons running in bundles just outside of the spinal cord (illustration). They show that axons actually are quite plump structures. You may have gained a different impression during the last laboratory period from looking at quite shriveled axons in peripheral nerves. Can you find some clusters of nonmyelinated axons in these rootlets? (illustration).
Because the preservation is so good you also get an extraordinary view of the ependymal cells lining the central canal in this slide.
D-192 spinal cord
D-192 and D-193 have cross-sections of spinal cord stained with two silver procedures. Both show the great complex of neuronal processes that make up the "neuropil," that is, the area where numerous synaptic connections occur, almost always in the gray matter. You may be able to trace short segments of axons and dendrites, and associate them with cell bodies in this preparation. I find it fascinating to look at the cells on these slides (#1, #2, #3, #4)..
Also examine the grey matter in slide D-193 (nice, but it doesn't beat D-192). The Bodian stain is a great one for distinguishing myelinated from nonmyelinated axons (remember from last lab period?) Some regions of white matter are made up primarily of myelinated axons. Others have mainly nonmyelinated ones. Be sure, to treat yourself to a peep at the rootlets on this slide. Here you cannot miss the difference between clumps of nonmyelinated axons and axons with myelin (illustration). If a person is interested primarily in counting the number of nerve fibers, or in their distribution according to size, the silver staining can be the method of choice, n'est-ce pas?
* * * * *
Cortexes of the brain
The brain is histologically and cytologically specialized in very particular ways. The outer part ("cortex") of both the cerebellum and cerebrum is comprised of gray matter organized in a laminar fashion with the white matter underneath. The gray matter contains neuronal cell bodies and their dendrites as well as glial cells. The white matter contains the outgoing axons of cortical neurons, incoming axons, and glial cells.
D-196 Cerebellar cortex
Hold this slide up and distinguish the gray matter on the surface (about 2 mm thick, with two obvious layers) from the white matter below (illustration). The highly cellular layer is called the granule cell layer. Granule cells are very small neurons with nuclei about the size and shape of lymphocytes. They send their axons unto the upper molecular layer. That layer is filled mainly with very fine axons and dendrites from the cells below. A few neurons called basket cells and stellate cells are scattered in the molecular layer. (Do not worry about distinguishing them from each other or from the glial cell nuclei in the molecular layer). A single layer of giant Purkinje cells lie at the boundary of these two layers. These are giant neurons. They send their dendrites into the molecular layer and their axons into the white matter for the main output from the cerebellar cortex. Appreciate the orderly layered organization of the cerebellar cortex.
D-197 Cerebellum (Bodian stain)
Although only the cell bodies can be seen in the H & E section, silver staining also shows up parts of their axonal and dendritic systems. Identify the three layers of the cerebellar cortex at low power (illustration). Then describe to your partners what you can make out about the orientation of the fibers in the cerebellum from this slide at high power (illustration). Your neuro course will go into the organization of the cerebellum in painful detail ("Hey, no pain, no gain", as our marathon runner Michael Hall is wont to say).
D-198 Cerebrum (Kluever stain)
The cerebral cortex, like the cerebellar cortex, is organized in folded layers of gray matter (illustration) overlying the white matter. This slide shows the density of cells in the cortex. The main neuron type is the pyramidal cell, which comes in various sizes. These cells usually have a prominent apical dendrite which points to the surface. The thinner axons project into the white matter from the deeper ends of these cells (the bases of the pyramids). Differences in the numbers and sizes of neurons allow the cerebral cortex to be subdivided into a series of layers I, II, III, ....(see your text). You can discern some of this layering on your slide but not well (illustration). These layers extend over the entire cerebrum, but subtle differences in composition allow the cortex from various regions of the cerebrum to be distinguished.
D-195 Cerebral cortex (stained for astrocytes)
A section of cerebrum was stained here with a particular silver technique to demonstrate astrocytes. Silver ions absorb onto their microfilaments, staining the entire astrocyte cell, not just its nucleus. You will find them well stained in some parts of the white matter, where conditions were just right.. They can just be seen under low power as spidery cells, totally blackened by the silver (illustration). Under high power, when suitably oriented, you can trace some of their processes for considerable distances, and in particular, find them making contact with capillaries (illustration). The capillaries are the empty spaces in the white matter.
This slide also shows the shape of the neurons in the cortex quite well. Aha! Now I see that they are called pyramidal cells because they have a cone of cytoplasm above the nucleus. Their dendritic pattern also can be somewhat faintly seen. Pyramidal cells have a large dendrite that extends upwards and smaller dendrites around the base. Their axon, which is hard to see, descends from the lowest part of the cell body. This stain shows a little bit better that the cortex is composed of layers with different cellular composition. Actually, this is a nice slide. Why didn't you look at it before D-198?
D-199 Choroid plexus (H&E)
The choroid plexus hangs down from the roof the ventricles in the brain. In this slide, you will find three masses of brain tissue stained with H & E. The two side cavities that you can see are parts of the lateral ventricles, sectioned coronally. A part of the third ventricle is shown vertically in the midline. These cavities are lined with an unspecialized low cuboidal ependyma. As the epithelium reflects (turns around and extends) over the choroid plexuses it becomes specialized for secretory purposes with larger cuboidal cells. The choroid plexus gives something of the appearance of a bunch of grapes * dangling into the ventricles (illustration). The core of each plexus is delicate connective tissue (pia) which is extremely well vascularized (illustration). This structure secretes cerebral spinal fluid, into the ventricular system, eventually to circulate in the subarachnoid space, and to be reabsorbed in arachnoid villi. Compare the ependymal cells lining the choroid plexus with those covering the walls of the ventricle. Similar but different, eh?
* I keep bringing up the analogy with grapes to keep up the spirits of Dr. Hall, a great admirer this fruit .....after it has been trampled under foot and bottled.