Sex differences in the foraging behaviour of adults have been observed in a number of sexually size‐dimorphic birds, and the usual inference has been that these sex‐specific differences are driven primarily by differences in body size. An alternative explanation is that foraging differences result from sex differences unrelated to size, such as sex‐specific nutritional requirements. To examine these alternative hypotheses, the foraging behaviour of parents was compared between two sympatric and congeneric species of seabird, the Brown Booby Sula leucogaster, which is highly sexually size‐dimorphic (females 38% larger) and the Red‐footed Booby S. sula, in which sex differences in body size are less marked (females 15% larger). Using temperature and depth loggers, we found that there were highly significant differences in the foraging trip durations and diving behaviour of male and female Brown Boobies. These sex differences were less marked in Red‐footed Boobies. Thus, our interspecies comparison revealed that the magnitude of the difference between the sexes matched the sexual size dimorphism of the species, providing support for the size hypothesis.

Until recent years many surgeons regarded general anasthesia as unsafe for intraocular surgery. Even in this country techniques such as intermittent thiopentone or local analgesia combined with small doses of curare were still being advocated as being safer, from the point of view of the eye, than full general anasthesial. Today few would consider that such techniques give the degree of control which is regarded as an essential part of modern anasthesia. Many surgeons now prefer full anasthesia and indeed the increasing scope of ophthalmic surgery demands it. The papers which have appeared in recent years reporting large series of intraocular operations carried out under general anasthesia suggest that the surgical results are neither better nor worse than those done under local, but there may well be an invisible gain, firstly in that patients are spared a trying ordeal and secondly that patients previously refused surgery because their co-operation was in doubt, are now having their sight restored by operations performed under general anasthesia.The purpose of this paper is to consider some of the factors which any form of anasthesia must take into account and to report some observations which were made, stimulated by the increasing demand of surgeons for general anaesthesia for their patients.In this type of surgery the control of intraocular pressure assumes as vital importance as the control of intracranial pressure does in neurosurgery and because the sclera, like the skull, is inelastic, the two have much in common. The factors controlling ocular tension have been well sumniarised recently by Carball02 and only some of them will be considered here.

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The cardiovascular actions of suxamethonium were studied in spinal cat preparations, and in cats with intact central nervous systems anaesthetized with a thiopentone, nitrous-oxide and oxygen sequence. Mechanical artificial ventilation of the lungs was maintained throughout. Intra-arterial pressure, standard limb lead electrocardiograms and respiratory movements were recorded. Under these conditions suxamethonium was shown to have nicotine-like and muscarine-like activity. It is suggested that suxamethonium produces similar effeas in other animals and in man.

A N E S T H E S I A 99to changes in central venous pressure. The converse conclusion by Marx ct nZ. 1 is we believe partly due to their method of expressing their mean results as percentage changes.The rapidity of the rise in CSF pressure on administering the volatile agent and of the fall on withdrawing it suggests that the CSF pressure changes were not the result of alterations in brain or CSF volumes but were due to abrupt changes in cerebral blood flow. This conclusion was supported by experiments in dogs in which cerebral venous pressure measured in the superior sagittal sinus increased pari passu with the CSF pressure during halothane administration. (The relationship of these findings to those obtained by direct measurements of cerebral blood flow was then discussed.)Jn another group of patients, hyperventilation was found to lower CSF pressure even when the control value was normal, in contrast to Rosomoff'sz and our own findings in dogs. Hypothermia also lowered CSF pressure despite the maintenance of a normal arterial Pco during cooling. When halothane was administered during hyperventilation or hypothermia only a very small increase in CSF pressure occurred.In conclusion, the rises in CSF pressure which occur with halothane or trichlorethylene administration appear large enough to be of clinical importance but these changes can be minimised by the concomitant use of hyperventilation.This study was supported by a grant from the Medical Research Council. In a clinical study in which intraocular pressure (IOP) was measured by Schitz tonometry during anzsthesia, it was shown that IOP remained unaltered throughout a wide range of physiological blood pressures, but lowering the mean pressure below about 90mm/Hg resulted in a fall in the pressure in the eye. Increasing the arterial Co2 tension caused a rise in IOP and decreasing it, a fall.