Sec.3.  But, although the thing to be sold has no actual and present existence; yet if its future existence is possible, and if it is the product or increase of something to which the seller has a present right, it is the subject of sale.  Thus, a man may sell the wool that may grow on his sheep, the fruit that may grow on his trees, or the future increase of his cattle.  But he cannot sell the products of the sheep or cattle which he may hereafter buy.  A man may, however, agree to procure goods which he has not, and to furnish at a future time, for a certain price; and his contract will be good; though this is not strictly a sale, but an agreement to sell.

Sec.4.  There can be no sale without a price; and the price must be fixed and definite, or susceptible of being ascertained by reference to some criterion prescribed in the contract, so as to render any further negotiation of the parties unnecessary.  Thus, a man may agree to pay what shall be the market price at a particular time, or a price to be fixed by a third person.  The price must also be payable in money or its negotiable representative, as notes or bills.  One article given for another is merely barter.  The same principles of law, however, govern in both cases.

Sec.5.  There must be a mutual consent of the parties, and the contract is binding when a proposition made by one party is accepted by the other.  The negotiation may be carried on by letter, as before stated. (Chap.  LIV, Sec.7.)

Sec.6.  In contracts of sale which are not perfected at once by payment and delivery, certain formalities are to be observed.  These forms generally are prescribed by what is called the English statute of frauds, which requires, (1.) that the buyer shall accept and receive part of the goods sold; or (2.) give something in earnest to bind the bargain, or in part payment; or (3.) that some note or memorandum in writing of the bargain shall be made and signed by the party to be charged, or by his authorized agent.  These provisions, however, apply only to cases in which the price of the goods sold is ten pounds sterling, or more.  The same rule prevails generally in this country, with slight variations in some states.  The price of the goods sold, in cases to which the provisions of that statute apply, is fixed by law in many of the states, and varies from $30 to $200.

Sec.7.  To complete a contract of sale, and pass the title to the property to the buyer, there must be a delivery of the goods sold.  When the goods are such as cannot be manually or immediately delivered, or are not in the actual custody of the seller, the law does not require an actual delivery.  But they must be placed in the power of the purchaser; or there must be such acts and declarations of the parties as imply a change of ownership.  When the right of property has been transferred to the buyer, whether by an actual or only a constructive delivery, he immediately assumes the risk of the goods; so that if they shall be afterward injured or destroyed, he must bear the loss.