This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This disease appears to be prevalent wherever the Apple is cultivated. The symptoms are: the presence of scattered brown or rust-coloured spots in the flesh of the apple, more especially towards the calyx or "eye" end of the fruit. When the spots are near the surface the skin sinks over the spots, and the apple presents the appearance of having had smallpox. No fungus nor insect is concerned with this disease, which is of a physiological nature, and no knowledge as to a cure or preventive is at present known. It has been suggested that, in new countries where the Apple is grown, it is due to the introduced trees having not as yet become acclimatized. This, however, is not a satisfactory explanation, as many kinds of Apple suffer severely in this country where the varieties were produced from trees that have been in existence here for ages.