As the result of some experiments reported last year,1 it was concluded that the sugar content of the normal vitreous was always considerably lower than that of the aqueous or blood serum of the same animal. The average blood sugar of cats was found to be 135 mg. per cent. The aqueous averaged 113 mg. per cent, while the vitreous averaged 64 mg. per cent. The samples of aqueous, blood and vitreous were drawn simultaneously, and careful tests were made of the reliability of the methods employed.
I was puzzled how to account for this low vitreous sugar. When the blood sugar of an animal was raised experimentally, the aqueous rapidly equilibrated itself to the new sugar level. The vitreous did so likewise, but being a gel the changes took place much more slowly. This proved, however, that the vitreous could increase its sugar level when