Abstract: Compounds of the formula ##STR1## and pharmaceutically acceptable non-toxic acid addition salts thereof, in which L and D, when applicable, define the chirality;R.sub.1 is hydrogen, C.sub.1 -C.sub.3 primary alkyl, or allyl;R.sub.2 is hydrogen or C.sub.1 -C.sub.3 primary alkyl, subject to the limitation that when R.sub.1 is allyl, R.sub.2 is hydrogen;R.sub.3 is hydrogen or C.sub.1 -C.sub.3 primary alkyl;R.sub.4 is C.sub.1 -C.sub.4 primary or secondary alkyl;R.sub.5 is hydrogen or C.sub.1 -C.sub.4 primary or secondary alkyl;R.sub.6 is hydrogen or C.sub.1 -C.sub.3 primary alkyl;R.sub.7 is hydrogen or C.sub.1 -C.sub.3 primary alkyl;Y is hydrogen or acetyl;Z is hydrogen of ##STR2## in which R.sub.8 is C.sub.1 -C.sub.3 alkyl or hydrogen; and W is isopropyl, --VR.sub.9, or --CH.sub.2 --X--CH.sub.3, in which V is O or S, R.sub.9 is C.sub.1 -C.sub.4 alkyl or aralkyl, and X is O, S, or --CH.sub.2 --, subject to the limitation that, when W is isopropyl, R.sub.7 is C.sub.1 -C.sub.

Abstract: Compounds of the formula ##STR1## and pharmaceutically acceptable non-toxic acid addition salts thereof, in which L and D define the chirality;R.sub.1 and R.sub.2 independently are hydrogen or C.sub.1 -C.sub.3 primary alkyl;R.sub.3 is C.sub.1 -C.sub.4 primary or secondary alkyl, C.sub.1 -C.sub.2 hydroxyalkyl, or --CH.sub.2 CH.sub.2 --U--CH.sub.3, in which U is O or S;R.sub.4 is C.sub.1 -C.sub.3 primary alkyl;Y is hydrogen or acetyl;Z is --CH.sub.2 OH or ##STR2## in which R.sub.5 is C.sub.1 -C.sub.3 alkyl or hydrogen; and W is isopropyl, --VR.sub.6, or --CH.sub.2 --X--CH.sub.3, in which V is O or S, R.sub.6 is C.sub.1 -C.sub.4 alkyl or aralkyl, and X is O, S, or CH.sub.2 --; are useful analgesic agents.

Abstract: A ventilated animal cage system is provided in which a plurality of animal cages are removably suspended on shelves of a portable rack. Each shelf is hollow to form an air duct that is in communication with the cages suspended therefrom, thus minimizing the possibility of cross-contamination between animals in the cages and personnel in the laboratory room.