Abstract: An added main line system is disclosed with particular utility in connection with equipment for providing the services of two telephone lines on a single conductor pair. The ring generator of the added main line system has two transistor bridges, one for the ringing signal on each of two subscriber lines. In each bridge, diagonally opposed pairs of transistors are turned on in alternation, providing alternating current for the ringing signal. The two bridges, each of which has four transistors, share two transistors. Comparators provide off-hook detection during the ringing cycle. Off-hook detection circuits are provided in series with selected driver transistors of the bridges, so that the condition of customer equipment going off-hook may be detected even though limited power is available for testing for the off-hook condition.

Abstract: Compounds comprising polypeptide derivatives of the formula ##STR1## wherein R.sub.1 is the amino acid sequence of the polypeptide minus the terminal amino acid; R is the side chain group determining the identity of the terminal amino acid; and Z is ##STR2## or --CH.sub.2 X wherein X is Cl, Br, or I; are provided. Precursor peptides are peptide hypothalamic releasing and inhibitory factors, opiate peptides, and fragments thereof. The derivatives act as antagonists or agonists to the precursor peptides and are particularly useful in bioassay procedures.