ULTRASTRUCTURE OF THE CAROTID-BODY OF THE GOAT

The carotid body of the goat was found to be a small oval or rounded p arenchymatous organ. It was characterized by its profound vascularity. Delicate septa divided the parenchyma into small feebly defined lobul es. Electron microscopy revealed that the parenchyma comprised type I cells, type II cells, nerve endings, axons and fenestrated dilated cap illaries. Type I cells were characterized with electron dense-cored ve sicles. They showed variations in size and concentration of the dense- cored vesicles and number of mitochondria. The possibility that these variations are reflections of different stages of activity is discusse d. Type II cells were less numerous than type I cells, relatively smal l and devoid of dense-cored vesicles. They usually surrounded small gr oups of type I cells and associated nerve endings and axons. Presumpti ve afferent nerve endings characterized with many clear vesicles, occa sional large granular vesicles and varying numbers of slender mitochon dria, lay apposed to type I cells. Nerve endings of this kind showed a fferent and efferent synaptic junctions with type I cells. Presumptive sympathetic efferent endings were occasionally seen within the lobule s but never lay apposed to type I cells or afferent nerve ending.