COLLES'S FRACTURE

cussion of the subject in these columns about a year ago 'namely, that there are now sufficient data to question the advisability of the routine use of prolonged high oxygen concentrations in the nursery. Of course, this does not go far enough, and clinical and laboratory investigations are proceeding in various centres in an effort to clarify the position. An interesting contribution to this work is a laboratory investigation by Norman Ashton et alii' into the influence of varying concentrations of oxygen upon the immature retina. The laboratory animal selected was the kitten, as the degree of retinal vascularization in the full-term kitten at birth and in the ensuing three weeks is comparable in extent to that of the premature baby. Bacteriological incubators were converted into gas chambers, into which oxygen was passed through an inlet tube; the flow was so adjusted as to provide a concentration of 75% to 80% of oxygen. The mother cat and test kittens were placed in the chamber and maintained in the experimental conditions for some days; at the end of each experiment the kittens were anresthetized, and after one eye had been removed for section, the left ventricle was injected with indian ink. The remaining injected eye was then removed and placed in fixative for twelve hours; after freezing it was opened transversely, and the retina was removed and mounted flat for study under the stereoscopic microscope. The findings indicate that high concentrations of oxygen are able to obliterate the ingrowing vessels in the developing retina of the kitten. Since the fully mature retina of the kitten was not affected, it would appear that this process represents a specific effect upon growing vessels or a fundamental interference with the process of vascularization. Obliteration of the vascular channels is irreversible in many vessels, and this appears to be due to some extent to the coagulation of entrapped blood. After the animal is. transferred to air, such vessels as remain patent refill with blood, but the resulting vascular architecture is grossly abnormal, consisting of an irregular cobweb of vessels without definition into arteries or veins, and extensive hremorrhages may appeal' at the periphery of the reopened network. New vessels are seen growing into the vitreous eighteen days after exposure to high concentrations of oxygen, and this is accompanied by retinal detachment thirty days after such exposure. The authors think it probable that similar obliteration of retinal vessels may occur in the premature infant, and that this may be the underlying cause of retrolental fibroplasia. While the basic injury of vascular obltterationis inflicted in high oxygen concentrations, the effect of this action is not evident until the animal returns to ordinary atmospheric conditions.