The leukocytes and platelets of Trichosurus vulpecula are in many respects typically mammalian. Relatively unusual morphological features are paucity of granules in neutrophils, elongated form of eosinophil granules, abundance and uniformity of basophil granules, and, in monocytes, high frequency of irregular nuclei (some annular) and coarseness of chromatin.
Mean leukocyte count per cmm was 13, 380 and mean counts for individual cell types were: neutrophils 5, 790, eosinophils 221, basophils 31, lymphocytes 6, 720, monocytes 619. The last two of these are fairly high amongst mammals, those for eosinophils and basophils fairly low. The mean number of nuclear segments per neutrophil was 2.41, per eosinophil 1.34. Mean diameters (in μ) of cell types in stained smears were: neutrophils 13.00, eosinophils 13.77, basophils 14.24, lymphocytes 10.32, monocytes 14.99. Most platelets are similar in size to human ones but large examples are more common.
Neutrophil granules are coloured intensely by sudan black B, eosinophil granules less so. Basophils and platelets, and most monocytes and lymphocytes, are sudanophobic.
Amylase-labile PAS-positive material is abundant in neutrophils; there is some in platelets and, probably, also in basophil cytoplasmic matrix. Basophil granules and the periphery of eosinophil granules exhibit amylase-resistant PAS-positivity.
No peroxidase is demonstrable in leukocytes using o-tolidine as substrate, but with benzidine a positive reaction occurs in neutrophils and eosinophils.
Alkaline phosphatase is demonstrable only in basophils-mostly in their specific granules, a location not previously reported for any mammal. The simultaneous coupling azo-dye method used was more sensitive and gave more precise localization than the cobalt sulphide technique.
Succinate dehydrogenase activity is exhibited by some lymphocytes, monocytes and platelets. Lactate dehydrogenase activity is more intense in these cells and, especially, in platelets; a weak reaction occurs in some neutrophils and eosinophils.

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The trigeminal mesencephalic nucleus was studied with an electron microscope after neurotomy of the third division of the trigeminal nerve in rats. Neuronal ultrastructures were characterized by the changes of the cell organelles 17hrs after neurotomy. Especially numerous polysomes appeared in the perinuclear area and then migrated into the peripheral area. Concomitantly, the central area of the cytoplasm was filled with bundles of synthesized neurofilaments. Ten days after neurotomy, the Nissl pattern shifted to dispersing free ribosomes and granular endoplasmic reticulum. Necrotic neurons and degenerating processes of the affected neurons revealed dense matrix and often lamellated dense bodies. These neurons packed with fibrous or tubular substances showed loss of the Nissl substances after 40 and 95 days. In the neuropil, astrocyte end feet accumulated more glycogen particles than usual. The vascular walls showed remarkable changes after 17hrs. Pericytes were activated as phagocytes, which have dense cytoplasmic matrix and large masses of lysosomal dense bodies and phagocytotic vesicles. Slight changes were observed in the vascular walls and perikarya of the neurons of the contralateral mesencephalic nucleus as well.

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The accessory thyroid glands distributed in the fatty tissues surrounding the ascending aorta of the dog were investigated by light and electron microscopy.
1. Out of the 45 dogs examined, 29 possessed one or more accessory thyroid glands, in the most numerous case six (Table 1). They were generally oval in form and measured 1-2mm in long diameter.
2. There was recognized not a single parafollicular cell in the accessory thyroids, although 26 glands were examined in serial sections and stained by silver impregnation, pseudoisocyanin and lead-hematoxylin known as the positive staining methods for the parafollicular cells. Otherwise, the light and electron microscopic structures of the accessory thyroids corresponded to those of the main thyroid glands.
3. The reactions under the light and electron microscopes of the follicular cells of the accessory thyroid to hypophysectomy and treatment of antithyroid drug were identical with those of the main thyroids.
4. After thyroidectomy, the accessory thyroids showed conspicuous hyperactivity. Although their morphological changes resembled those of the animals injected with antithyroid drug, they scarcely proliferated.
5. In dogs with induced hypercalcemia the accessory thyroid glands were not affected at all.
6. The present study indicates that the follicular cells and parafollicular cells were of distinct cell lines and that the accessory thyroid glands may be separated from the main thyroid before the latter incorporates the ultimobranchial body.

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The globules in goblet cells in the epithelium of the dog ileum show a moderate contrast between the light and dark types. The globules appear to arise from the Golgi apparatus. Membranes encapsulate all of the globules in the earlier stages but a part of the mucosubstance undergoes a dispersion or, in some cases, possibly a fusion before their discharge into the intestinal lumen. There is little evidence of any escape of organelles into the lumen during secretion and the residual cytoplasm is always limited by a continuous membrane when the goblet is emptied. The residual portion of the cytoplasm appears to be functionally active at the stage when the goblet has been effectively emptied. Both the Golgi apparatus and the rough surfaced endoplasmic reticulum contain a substance similar to that in the light globules . The discharged mucus is distinctly different in appearance from the glycocalyx of the microvilli of nearby absorptive cells.

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Small pieces cut from the spinal cord of the rabbit were fixed and dehydrated and embedded in gelatin capsules filled with Cemedine 1500. The Cemedine was hardened at -30°C and the capsules were cracked into two pieces. The cracked surface of the specimen was observed under the scanning electron microscope.
1. In the cytoplasm of the anterior horn cell the Nissl bodies were observed like specks. The Nissl bodies were denser than the cytoplasm surrounding them and contained numerous granuies (about 400Å in diameter) and membranous structures oriented parallel to each other. In the cytoplasm corresponding to the Golgi regions many vesicles and cisternal and membranous structures could be seen. On the surface of nerve cell bodies small swollen terminations of axons, which seemed to be end-bulbs, were observed.
2. The membranes consisting of myelin sheaths, which surrounded the axon as a whirlpool, were observed in three dimensions. The myelin sheath sometimes extended thinner processes which could be considered to be the cytoplasmic processes of the neuroglial cell.
3. The cilia covering the ependymal cells of the central canal were fairly uniform in number (12-15) from cell to cell, and were arranged in a tuft for each cell. The surface was also rich in microvilli which formed various shapes.

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