You will have to reduce the item "feed" to many items, and remember that hay produced at home is not free hay. It is worth to feed to Roberta just what you would have to pay wholesale for it if you had to go to the feed store, minus the cost of cartage. To work this out is good arithmetic, better than covering acres of blackboard space with examples in "partial payments." Now Roberta may give a good quantity of milk but of poor quality. At first you might think that didn't matter; it brings just as much a quart. But does it, when your mother and sisters make it into butter, for example? Or, if you sell cream, wouldn't you want a cow whose milk tested high in butter fat? Your customers would, whether they bought milk or cream, I know. [Illustration: Photograph by Julian A. Dimock. Holding a Conversation] The boys and girls in many of the great dairying states, notably Illinois and Wisconsin and New York, are learning in school how to test milk for the butter fat it contains and the chances are that every agricultural college in the United States is ready to instruct boys and girls by letter in this important part of dairying. Many of them send out printed lessons giving careful directions about using the Babcock testing apparatus, and I have seen a class of boys and girls in a country school testing milk from their fathers' cows. It is astonishing how many cows are kept on farms purely for ornament--or maybe to give the boys plenty of chores. These cows consume as much food as good ones, but they are idlers. It isn't their fault but the farmer's. Can your father or you afford to keep money invested in any cow that returns him less than a dollar a year over and above the expense of feed? A good cow may cost twice as much to buy, but a good cow will make thirty or forty dollars a year clear gain. These figures are not guess-work but facts.