A variety of inert materials have been inserted into fish stomachs to obtain samples of gastric juices. Spongey foam plastic has been inserted under anaesthesia and removed later. The contents of the sponge were then squeezed out and analyzed for acid and enzyme content. Glass beads were inserted into the fish stomachs to test the effects of stomach distension. A disadvantage of both methods was that the inserted materials were much easier to acidify (not as well buffered) than food, and that the stomach may not have responded to them in typical fashion.