MEDLEARN: a computer-assisted instruction (CAI) program for MEDLARS.

*MEDLEARN*, a second-generation computer-assisted instruction (CAI) program available (nationally) since October 1976, provides on-line training for MEDLINE, one of the National Library of Medicine's (NLM) Medical Literature Analysis and Retrieval System (MEDLARS) data base. *MEDLEARN* was developed as a joint effort between NLM and The George Washington University Medical Center. Using MEDLINE formats throughout, *MEDLEARN* combines tutorial dialogue, drill and practice, testing, and simulation.

MEDLEARN:an orientation to MEDLINE.

(***)MEDLEARN(***), an orientation to MEDLINE, was developed to educate members of the biomedical community to become competent on-line searchers. It appears in two complementary forms: an interactive terminal presentation available on the TYMSHARE Network and a supporting hard-copy manual which contains the didactic portions of the computer program as well as additional items which are not suitable for on-line presentation. (***)MEDLEARN(***), a flexible instructional tool, is divided into forty sections which may be selected in various sequences depending on the user's previous experience.

Cellular mechanism of intestinal permeability alterations produced by chelation depletion.

The absorption of phenolsulfonphthalein (phenol red) was used as a measure in vivo of intestinal permeability in anesthetized rats. A chelating agent, sodium ethylenediaminetetraacetate (NaEDTA), placed in the lumen evoked a fivefold increase in membrane permeability; at the same time the mucosal content of magnesium and calcium decreased significantly. Making either magnesium or calcium available to the luminal surface of the membrane in isotonic solution restored normal permeability and brought the cation contents above the original levels.