30 HARVARD LAW REVIEW ' issuer in praesenti without complying with impracticable terms of the letter, yet obviously he could not sue and enforce that claim without the letter. In such a case, on established principles, the pledgee of the paper would have an equitable lien.^^ Where business changes take place the case is more difficult. For reasons already set forth there is no help in such a case on theories of offer, or guarantee, or contract for the benefit of a third person. If we think of the letter as an acknowledgment of money held to the use of the addressee upon condition, we must ask whether the condition can be performed. And this resolves itself into a question whether the buyer-seller contract may be assigned. If that contract can be assigned to and enforced by the business suc- cessor, it is submitted that the latter may perform the conditions of the letter and enforce it. Ordinarily when such business changes take place the parties no doubt will take care to make an express agreement obviating such questions. But if the buyer-holder^should seek to take advantage of the situation to escape from his contract and hence refuse to enter into or sanction a new agreement, the point might well be important. In case of sub-contracts, what has been said as to pledge of the letter by the addressee becomes apphcable. The addressee, where there is a sub-contract given by him, may deposit the letter with the sub-contractor which will raise the same questions as the deposit of the letter for security. Where there are a number of sub-contracts, so that this course is not possible, the addressee might deposit the letter with a trustee for the benefit of the sub-contractors according to their several interests. But the usual plan is to deposit the letter with a bank as security and ask the bank to issue new letters of credit addressed to each of the several sub-contractors. A letter which is expressly made assignable raises questions like those which arise upon a general letter. Such an instrument amounts to a letter addressed to the addressee or to such person or persons as he may turn it over to. Or, if the letter is in the form of authority to draw, it amounts to a power conferred on the ad- dressee to designate those who may avail themselves of the oflfer. Letters sometimes contain express powers of designation of this ^8 Harrison v. McConkey, i Md. Ch. 34 (1847); Ruckman v. Ruckman, 33 N. J. Eq. 354 (1880); Pringle v. Pringle, 59 Pa. St. 281 (1868); Pierce v. Bank, 129 Mass. 425 (1880); Hill V. Stevenson, 63 Me. 364 (1873).
