SUMMARY The movement of water to and from the vitreous across the retina and pigment epithelium is important in relation to an understanding of such conditions as retinal detachment and its surgical cure, central serous retinopathy, and retinal oedema. Experiments were carried out to determine the main routes for removal of water injected into the vitreous and to see if the removal could be explained on the basis of diffusion or whether bulk flow was also implicated. 25 ,uCi of 3H20 in 25 IlI were injected into a central position in the vitreous humour of living rabbits under general anaesthesia. For 9 animals blood was collected from one of the 4 vortex veins draining the choroid and the radioactivity in the samples measured. For another 6 rabbits similarly injected the radioactivity in samples of aqueous humour was determined. The percentage of injectate recovered from the vortex vein blood ranged between 13% and 38%, mean 25+±3%. The percentage of injectate recovered from the aqueous humour ranged between 1 2% and 5 2%, mean 2-8±0-6%. Analysis of the time course of isotope activity in the samples revealed a mean transit time from the mid vitreous to the choroid of 32+2 minutes, and from the mid vitreous to the anterior chamber of 84±3 minutes. By means of a computer model it was calculated that diffusion alone could effect this transfer; if active transport were involved in the transport of 3H20 to the choroid, this was not a limiting factor under the conditions of the experiment. reported work on molecular movement from the vitreous has used a variety of tracers, some of which might have been subject to the processes of active transport, or differed from water in intermolecular interactions or in molecular size.Diffusional exchange with the water in the anterior chamber, which is largely cleared by bulk flow through the outflow apparatus, is another factor which might influence the clearance of water from the vitreous.As part of a study of water movement in the eye, experiments were carried out to: (1) determine the main routes of clearance of 3H20 injected into the midvitreous of living rabbit eyes and to quantify the movement via each of these routes; (2) determine by comparison with a mathematical model whether any detected movements of water could be explained entirely by diffusion or whether active transport or bulk flow were involved. The results of these studies are presented in this paper. 145

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Human fingernail thickness was measured distally in 39 subjects using an adapted electronic micrometer and ultrasound transmission time was measured both distally and proximally. Distal ultrasound nail transmission time correlated well with micrometer measurements. There was a clear rank order of distal and proximal nail transmission times: thumb greater than index greater than middle greater than ring greater than little fingers. Male nails had greater transmission times than female nails on the ring and little fingers. Distal nail transmission time was 8.8% less than proximal transmission time.

A Neodymium-yttrium aluminium garnet (Nd-YAG) pulsed laser was used in vitro to determine whether various laser energy levels from 0.75 W to 1.7 W at 15 pulses s(-1) (pps) were able to (i) remove debris from the walls of prepared root canals (ii) remove pulpal tissue from unprepared canals and (iii) create a fused apical plug from dentine chips, hydroxyapatite (HAP) or low-fusing dental porcelain. Single-rooted teeth were sectioned at the amelocemental junction and the crowns discarded. The root canals of 50 teeth were prepared chemomechanically and allocated to four groups of 10 teeth for laser treatment. One group was left unlased as a control. After lasing, the teeth were split longitudinally, stained and examined for residual debris. Results showed that there was no statistically significant difference between the groups (P<0.05). A further 20 teeth were not prepared and lased in the coronal one-third of the root canal at different energy levels; five teeth were not lased. The teeth were split and examined as previously. The results showed that lasing cleaned the coronal part of the root canal almost completely of pulpal tissue. In the final part of the study laser energy was applied to dentine chips, HAP and low-fusing porcelain in an attempt to produce a fused apical plug. The laser was unable to melt the dentine chips but some hardening of HAP occurred when combined with blue food-colouring, with or without glycerine, at energy levels of 1.0 W, at 15 pps for 30 s. Superficial hardening of low-fusing porcelain occurred at 1.0 W, 15 pps for 30 s.