3.25 in. x 4 in. Lantern Slides and The guinea pig pancreatic lobule preparation was developed in the laboratory of Dr. Jamieson at the Rockefeller. It was later adapted in these studies to demonstrate that newly synthesized exocrine pancreatic enzymes and proenzymes are packaged into condensing vacuoles and zymogen granules in synchrony, and are secreted in parallel upon stimulation in vitro by secretagogues. The advantage of the lobule preparation was rapidity of harvesting lobules in sufficient numbers for morphologic studies and cell fractionation with superior preservation of structural and functional characteristics over prolonged (12 hr. or more) incubation periods in vitro.