A quantitative light microscopic study has been carried out on the myenteric and submucosal ganglia of the stomach, duodenum, ileum, proximal colon and rectum of the guinea-pig; the enteric ganglia of the ileum were studied also in the mouse, rabbit and sheep. The area of the profiles of nerve cells, of nerve cell nuclei and of glial nuclei, and the proportion of the area of ganglia occupied by neuropil were measured, and the relative numbers of neurons and glial cells were estimated. The myenteric ganglia were found to be firmly anchored to the stroma of the muscle coat; their shape and the shape of their component cells varied with contraction and distension of the musculature. The range of neuronal sizes in the myenteric ganglia was extremely wide. In the guinea-pig, the myenteric neurons were on average largest in the stomach and duodenum and smallest in the ileum, with intermediate values in the colon and rectum; the submucosal neurons showed little variation in average size along the length of the gut. The average size of ganglion neurons in the ileum was greatest in the sheep and smallest in the mouse, and had intermediate values in the guinea-pig and rabbit. The percentage volume of neuropil in the myenteric ganglia was 51% in the mouse, 65% in the guinea-pig, 70% in the rabbit, and 74% in the sheep. The number of glial cells relative to the number of neurons was also ranked in the same order. In all the species examined the submucosal ganglia, when compared with the corresponding myenteric ganglia, had a smaller percentage volume of neuropil, a much smaller number of glial cells and (except in the mouse ileum) neurons of smaller average size. In all the ganglia there was a positive correlation between size of neurons and size of glial cells. The results are discussed in the light of possible relations between body size (and length of the intestine), numerical density of ganglion neurons, average size of neurons, amount of musculature, average distance between neurons, and amount of neuropil.

A new method was developed to define the distribution of mast cells in normal human skin. The population density was determined in a number of zones of different depth in the dermis. Two regions of the same limb were studied systematically. Both were shown to have mast cell populations of similar size and distribution, with a maximum density immediately below the dermo-epidermal junction, gradually falling to a minimum density in the deeper layers of the dermis. Small secondary peaks were less clearly defined at the base of the dermis. These findings should provide baseline data for comparisons with mast cell population size and distribution in different areas of normal skin, or in similar areas in clinical disorders or experimental conditions.

Neurons and glial cells of the superior cervical ganglion of sheep were investigated with morphometric methods in the light and electron microscope. The nerve cell sectional area (measured on nucleated cell profiles) ranged from 165 to 2500 microns2, which corresponds to range in cell diameter from 14 to 56 microns and a range in cell volume from 1600 to 93,000 microns3, i.e. a 60-fold volume difference between smallest and largest neurons. The distribution of cell sizes appeared unimodal, with a predominance of small neurons; there were no variations in different parts of the ganglion. This wide range in nerve cell sizes is discussed in the light of the suggestion that large neurons innervate a greater amount of target tissue (e.g. smooth muscle) and are less readily excitable than smaller neurons: it is thus possible that there is differential recruitment of ganglion neurons in autonomic reflexes. The ultrastructural features of ganglion neurons in the sheep were similar to those observed in small laboratory animals. The relative volumes of perikaryal cytoplasm occupied by mitochondria and Golgi apparatus were 8.5% and 4.8%, respectively, but the average values were the same in small and large neurons. Subsurface cisternae of endoplasmic reticulum were common in the perikaryon, while in the dendrites clusters of synaptic vesicles were found beneath the plasma membrane; the absence of a glial wrapping at the latter sites suggests that they are points of (non-synaptic) release of transmitters. The extent of the capsule that satellite cells form around each neurons was compared in size-based classes of neurons. There was no difference in the size of glial nuclei, and this suggests that glial cells are probably of uniform size. However, glial cells were more densely packed over the surface of large neurons than over the surface of small neurons--in fact the packing density was proportional to the ganglion neuron volume, rather than to its surface. The average thickness of the glial capsule was significantly greater around large than around small neurons. It is suggested that the matching of glial cell number and nerve cell volume is achieved during development by glial cell mitosis taking place long after the nerve cells have ceased dividing.

Cryostat sections from 160 rectal suction biopsies were stained for cholinesterases by the method of Karnovsky and Roots (1964) in an attempt to facilitate the diagnosis of Hirschsprung's disease.The method proved at least as reliable as experienced assessment of paraffin haematoxylin-eosin sections, and appeared to offer the advantages of reduced scanning fatigue and superior demonstration of the increased cholinesterase-positive nerves in Hirschprung's disease.Contrary to the findings of Meier-Ruge (1971) it was not possible to base a diagnosis on mucosal cholinesterase activity.