It is very well known that milk records show a considerable downward trend in yield from the East to the West of England and Wales. The Bureau of Records of the Milk Marketing Board have produced some admirable maps, shaded by counties according to the average yield, and these bring out the trend very clearly ; roughly the yield declines from 730 to 630 gallons, a drop of 15 per cent. This trend in yield is not a new phenomenon. Twenty-five years ago Dr. Hammond and I found the same thing with 26 counties which by 1923 had had milk recording societies functioning for five years ; the decline was approximately from 700 to 600 gallons. We selected two societies which were at that time about at the extremes and extracted lactation figures from the milk record books of the members in an effort to probe a little deeper into the difference. I hope to refer to these two again and will only say now that Norfolk milk recorded cows gave 22.8 per cent, more milk than those of Penrith, and of this difference, 6 per cent, was due to higher yield at the start of the lactation and the rest to greater persistence of yield and to longer continued milk flow.