Summary Reasons for performing study: Mucosal ulcers and, occasionally, small granulomas on the axial surface of one or both arytenoid cartilages have been found in TB yearlings presented for post sale endoscopic examination. Objectives: To determine the incidence, endoscopic characteristics and outcome of a group of Thoroughbred yearlings affected with mucosal ulcers and granulomas of the arytenoid cartilage. Hypothesis: The incidence of mucosal ulceration of the arytenoid cartilages of yearling Thoroughbreds is relatively high compared to other upper airway abnormalities; and that the majority of mucosal ulcers heal uneventfully, although a small percentage may progress to a granuloma and, less commonly, to arytenoid chondropathy. Methods: The findings of post sale, upper airway endoscopic examinations of 3312 Thoroughbred yearlings, during a 5 year period, were reviewed, including those abnormalities listed in the conditions of sale and others not listed but considered likely to cause airway obstruction. Information obtained from the medical record of horses that had mucosal ulceration or granuloma of the arytenoid cartilage included the location and size of the lesion(s), sex of the affected horse and the presence and nature of other concurrent abnormalities of the upper portion of the respiratory tract. Additional information included treatment and results of follow‐up, endoscopic examination by the authors or attending veterinarian. Results: Mucosal lesions were seen in 0.63% of yearlings evaluated, which represented the most common, documented condition of the upper portion of the respiratory tract. The mucosal ulcers of 15 of 19 horses were considered to have healed without complication during follow‐up examination; one of the 19 horses was lost to follow‐up. Two horses affected with bilateral, arytenoid mucosal ulceration developed a granuloma at each site of ulceration. One horse developed a granuloma at a site of ulceration and, subsequently, arytenoid chondropathy. Conclusions: Arytenoid mucosal ulceration in sales yearlings was a relatively commonly encountered abnormality and a small percentage progressed to granuloma or chondropathy. Potential relevance: The mucosa of the arytenoid cartilage, particularly at the rostral margin of the vocal process, should be examined carefully during endoscopic examination of the upper portion of the respiratory tract of Thoroughbred yearlings presented for sale. Because a small percentage of mucosal ulcers may progress to granuloma or, less commonly, chondropathy, identification of mucosal ulcers of the arytenoid cartilage seen during post sale, endoscopic examination warrants notification to the purchaser and sales company. Medical therapy of affected horses should be considered and follow‐up endoscopic examination performed to determine if the lesion has healed.

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PRE-BREAKDOWN currents in vacuum-insulated systems are usually regarded as due to field emission. If the electrodes are not subjected to heat treatment, however, these currents occur at unexpectedly low field strengths. We have recently examined a form of conduction at 10-150 kV. D.C. across gaps of a few centimetres in continuously evacuated systems. The current is in this case distinct from field emission because (i) it is critically dependent on anode conditions, and (ii) the voltage required is only slightly changed by large variations in gap-length. Other characteristics of interest are that the current is selfextinguishing, after a charge of the order of microcoulombs has crossed the gap, with only slight drop in voltage ; and that the voltage required may be increased by factors up to 2 by increasing the pressure of residual gas in the system.The mechanism of the conduction is still being investigated ; but it is clear that there is a resemblance to the 'electron loading' experienced in accelerating tubes in the megavolt field. It is hoped to publish a detailed report shortly.We wish to thank the Director of the Atomic Energy Research Establishment, Harwell, and the Ministry of Supply for supporting the work and for permission to publish the results.